Cnt-based sensors:  devices, processes and uses thereof

ABSTRACT

Disclosed herein are methods of preparing and using doped MWNT electrodes, sensors and field-effect transistors. Devices incorporating doped MWNT electrodes, sensors and field-effect transistors are also disclosed.

CROSS REFERENCE TO RELATED PATENT APPLICATIONS

This patent application claims the benefit of U.S. Provisional PatentApplication Ser. No. 60/762,788, for “CNT-Based Sensors: Devices,Processes and Uses Thereof”, by Salvator Pace, filed Jan. 26, 2006, theentirety of which is incorporated by reference herein.

FIELD OF THE INVENTION

The present invention is in the field of chemical and biologicalsensors. The present invention is also in the field of processes formaking chemical and biological sensors. The present invention is also inthe field of using sensors for monitoring water quality.

BACKGROUND OF THE INVENTION

Chemical and biological sensors that are used for continuous monitoringgenerally require a degree of inertness from the sample environment.Inertness is particularly important in utility type applications such aswater monitoring. Continually operating sensors in the field need to berugged, chemically stable and readily manufactured. There is acontinuing need to prepare and design sensors that can effectively andefficiently measure a wide range of chemical and biological contaminantsin drinking water in view of both public health and national safetyperspectives.

The low salt content (high electrical impedance) of drinking waterpresents a unique challenge to electrochemical measurement because smallvariations in electrolyte content will introduce significant measurementerror. Improvements in the ability to measure variable conductivitywater samples from drinking water to sea water without analyticalperformance degradation are presently needed. Even gold or gold-coatedelectrodes are known to degrade in such environments. Accordingly,improvements in electrodes and sensors are required.

U.S. Pat. No. 6,905,655 to Gabriel et al. discloses sensors that operateon the principle that the electrical conductivity of a MWNT changesdepending on the environment surrounding nanotube. The disclosedsensors, however, require one to carefully lay down MWNTs (“CNTs”)parallel to the surface of a substrate. Nanotubes oriented in such afashion are required to make electrical contact with two or moreelectrodes on the substrate through the outer surface of its graphenesheet. Such sensors typically require that the nanotubes are bonded withsome type of protective coating, such as a polymer, where the nanotubescontact the electrodes. In view of the difficulty of adhering nanotubeslying across electrodes in this fashion, there remains the need toprovide CNT-based sensors that overcome these difficulties.

Li et al., Nano Letters, 2003, Vol. 3, No. 5, 597-602, discloses acarbon nanotube electrode array for ultrasensitive DNA detection. Thenanoelectrode array is based on multiwalled carbon nanotubes embedded inSiO2, with only the open ends of the multiwalled carbon nanotubes beingexposed to the environment to give rise to DNA detection. Accordingly,only a very low surface area is provided in the carbon nanotubeelectrode arrays provided by Li et al. Further improvements are neededto enhance the sensitivity of carbon nanotube electrodes and sensors.

SUMMARY OF THE INVENTION

In certain aspects, the present invention provides sensors composed ofone or more multiwall MWNT (“MWNT”) array electrodes that are rugged inuse, chemically stable and readily manufactured. The MWNT arrayelectrodes used in aspects of the invention can be used to measuredrinking water compositions. Various sensor embodiments as describedherein can be adapted to many other applications, for example, inmedical testing of biological fluids, as well as in testing the safetyof pharmaceuticals, beverages and food.

In one aspect, the present invention provides antennae assemblyelectrodes, comprising: an electrically conductive layer at leastpartially surmounting a substrate; and an assembly of doped antennaevertically oriented with respect to the electrically conductive layer,wherein each of the doped antennae comprises a doped MWNT comprising: abase end attached to the electrically conductive layer, a mid-sectioncomprising an outer surface surrounding a lumen, wherein at least aportion of the outer surface of the mid-section is capable of being influidic contact with an environment in contact with the antennae; a topend disposed opposite to the base end, and a dopant attached to orcontained within the lumen, a dopant attached to or contained within theouter surface, a dopant attached to or contained within the top end, orany combination thereof. Sensors and field-effect transistors comprisingthese antennae assembly electrodes are also provided.

The present invention also provides methods of making an antennaeassembly electrode, comprising the steps of: surmounting a substratewith an electrically conductive layer; surmounting an assembly ofantennae on the electrically conductive layer giving rise to theantennae being vertically oriented with respect to the electricallyconductive layer, wherein each of the antennae comprises a MWNTcomprising a base end being attached to the electrically conductivelayer; a mid-section comprising an outer surface surrounding a lumen,wherein at least a portion of the outer surface of the mid-section iscapable of being in fluidic contact with an environment in contact withthe antennae; and a top end being disposed opposite to the base end; anddoping at least a portion of the MWNT with a cladding, a covalent bondlinkage, a functional dopant molecule, a fill material, or anycombination thereof. Doped antennae assembly electrodes, sensors andfield-effect transistors are also provided using these methods.

In other aspects, the present invention provides antennae assemblyfield-effect transistors, comprising: a substrate comprising a sourceand a drain; a gate oxide layer at least partially surmounting thesubstrate, source and drain; an electrically conductive layer at leastpartially surmounting the gate oxide layer; and an assembly of dopedMWNT antennae vertically oriented with respect to the electricallyconductive layer.

The present invention also provides sensors, comprising: at least twoelectrodes situated on a substrate, wherein at least one of theelectrodes comprises an antennae assembly electrode, wherein theantennae assembly electrode comprises an electrically conductive layerat least partially surmounting a substrate; and an assembly of dopedantennae vertically oriented with respect to the electrically conductivelayer, wherein each of the doped antennae comprises a doped MWNTcomprising: a base end attached to the electrically conductive layer, amid-section comprising an outer surface surrounding a lumen, wherein atleast a portion of the outer surface of the mid-section is capable ofbeing in fluidic contact with an environment in contact with theantennae; a top end disposed opposite to the base end, and a dopantattached to or contained within the lumen, a dopant attached to orcontained within the outer surface, a dopant attached to or containedwith the top end, or any combination thereof.

In other aspects, the present invention provides antennae assemblyelectrodes, comprising: an electrically conductive layer at leastpartially surmounting a substrate; and an assembly of antennaevertically oriented with respect to the electrically conductive layer,wherein each of the antennae comprises a MWNT comprising: a base endattached to the electrically conductive layer, a mid-section comprisingan outer surface surrounding a lumen, wherein at least a portion of theouter surface of the mid-section is capable of being in fluidic contactwith an environment in contact with the antennae; and a top end disposedopposite to the base end. Sensors and field-effect transistors are alsoprovided using these electrodes.

The present invention also provides methods of making an antennaeassembly electrode, comprising the steps of surmounting a substrate withan electrically conductive layer; and surmounting an assembly ofantennae on the electrically conductive layer giving rise to theantennae being vertically oriented with respect to the electricallyconductive layer, wherein each of the antennae comprises a MWNTcomprising a base end being attached to the electrically conductivelayer; a mid-section comprising an outer surface surrounding a lumen;and a top end being disposed opposite to the base end.

The present invention also provides methods of growing non-aligned MWNTson a substrate, comprising: depositing a nickel metal catalyst on asubstrate; and contacting the nickel metal catalyst with a gas mixturecomprising a carrier gas and a carbon source gas at a temperature in therange of from about 650° C. to about 750° C., the carbon source gascomprising acetylene, wherein the substrate comprises silicon, silicondioxide, silicon nitride, phosphorus doped poly silicon, or boron dopedP-type silicon, to give rise to non-aligned MWNTs attached to the nickelmetal catalyst.

The present invention also provides methods of growing aligned MWNTs ona substrate, comprising: contacting a substrate with a gas comprising acarrier gas and a carbon source gas at a temperature in the range offrom about 800° C. to about 960° C., the carbon source gas comprisingiron (II) phthalocyanine, wherein the substrate comprises silicon,silicon dioxide, silicon nitride, phosphorus doped poly silicon, orboron doped P-type silicon, to give rise to aligned MWNTs attached tothe substrate.

The present invention also provides methods of growing aligned MWNTs ona substrate, comprising: depositing a nickel metal catalyst on thetitanium barrier layer; and contacting the nickel metal catalyst with agas mixture comprising a carrier gas and a carbon source gas at atemperature in the range of from about 650° C. to about 750° C., thecarrier gas comprising argon, ammonia and hydrogen, the carbon sourcegas comprising acetylene, wherein the substrate comprises silicon,silicon dioxide, silicon nitride, phosphorus doped poly silicon, orboron doped P-type silicon, to give rise to aligned MWNTs attached tothe nickel metal catalyst.

The general description and the following detailed description areexemplary and explanatory only and are not restrictive of the invention,as defined in the appended claims. Other aspects of the presentinvention will be apparent to those skilled in the art in view of thedetailed description of the invention as provided herein.

BRIEF DESCRIPTION OF THE DRAWINGS

The summary, as well as the following detailed description, is furtherunderstood when read in conjunction with the appended drawings. For thepurpose of illustrating the invention, there are shown in the drawingsexemplary embodiments of the invention; however, the invention is notlimited to the specific methods, compositions, and devices disclosed. Inaddition, the drawings are not necessarily drawn to scale. In thedrawings:

FIG. 1A is a top-view perspective schematic illustration of anembodiment of a CNT array electrode of the present invention;

FIG. 1B is a side-view schematic illustration of the CNT array electrodeof FIG. 1A;

FIG. 2A is a top-view perspective schematic illustration of anembodiment of a CNT array FET, which is suitable for ion sensing, of thepresent invention;

FIG. 2B is a side-view schematic illustration of the CNT array FET ofFIG. 2A;

FIG. 3A is a top-view perspective schematic illustration of anembodiment of a CNT island array electrode of the present invention;

FIG. 3B is a side-view schematic illustration of the CNT island arrayelectrode of FIG. 3A;

FIG. 4 is a schematic illustration of an embodiment of a multi-sensorCNT array chip of the present invention that includes integrated counterand reference electrode elements;

FIG. 5 is a schematic illustration of a cladded CNT peapod used invarious embodiments of the present invention;

FIG. 6 provides illustrations of representative polymers that can beused as cladding and peapod materials for CNTs.

FIG. 7 provides illustrations of representative donor-acceptor polymerchemistries for CNT dopants;

FIG. 8A provides a schematic illustration of an embodiment of an elementof a peapod CNT array FET of the present invention that can be used as acalcium ion selective sensor;

FIG. 8B provides a schematic illustration of an embodiment of an elementof a cladded peapod CNT array FET of the present invention that can beused as an ammonia ion selective sensor;

FIG. 9 provides a schematic illustration of an embodiment of the methodof the present invention for making a CNT array electrode;

FIGS. 10 a-10 r provides a schematic illustration of an embodiment ofthe method of the present invention for making a CNT array FET;

FIG. 11 provides a schematic illustration of an embodiment of the methodof the present invention for making a CNT island array electrode;

FIG. 12 provides a schematic illustration of a suitable CVD furnace andauxiliary equipment for preparing CNT array electrodes of the presentinvention;

FIG. 13 provides a schematic illustration of equipment suitable forradio frequency sputtering and plasma polymerization of polymer claddingmaterials used in various embodiments of the present invention.

FIG. 14 shows a fabrication process of catalyst insulation andmechanical support.

FIG. 14I setup for thermal chemical vapor deposition

FIG. 14J shows aligned multiewalled carbon nanotubes (ACNTs) grown onPatterned Chip with growth conditions; Ar/H₂/Temp/FePc/Time:80/75/902/0.6/5 min.

FIG. 14K shows ACNTs grown on Patterned Chip with growth conditions;Ar/H₂/Temp/FePc/Time: 20/20/902/0.4/20 min.

FIG. 14L shows ACNTs grown on Patterned Chip with growth conditions;Ar/H₂/Temp/FePc/Time: 20/20/902/0.4/20 min. And post-clean up processcarried out to remove the sacrificial Copper layer.

FIG. 14M shows ACNTs grown on Patterned Chip with growth conditions;Ar/H₂/Temp/FePc/Time: 20/20/902/0.4/20 min. And post-clean up processcarried out to remove the sacrificial Copper layer.

FIG. 15A shows Non-aligned multiwalled CNTs grown on 30 nm Ni onPoly-silicon with gas ratio of Ar/H₂/C₂H₂: 100/20/15 sccm at 745° C.

FIG. 15B shows Non-aligned multiwalled CNTs grown on 30 nm Ni on P-typesilicon with gas ratio of Ar/H₂/C₂H₂; 100/20/15 sccm at 745° C.

FIG. 15C shows Non-aligned patterned CNTs grown on 60 nm Ni on crackedPoly-silicon with gas ratio of Ar/H₂/C₂H₂; 100/20/15 at 745° C.

FIG. 15D shows aligned multiwalled CNTs carpet (approximately 10 micronlong) grown on Poly Si/Ti 50 nm/Ni 30 nm (sample was annealed at 400° C.for 15 hours) with gas ratio of Ar/H₂/C₂H₂; 100/20/15 sccm at 745° C.

FIG. 15E shows aligned multiwalled CNTs carpet (approximately 35 micronlong) grown on Poly Si/Ti 50 nm/Ni 30 nm (sample was annealed at 400° C.for 15 hours) with gas ratio of Ar/H₂/C₂H₂; 80/75/15 sccm at 745° C.

FIG. 15F shows 35 micron long ACNTs bundle scratch off from thesubstrate. Growth conditions same as described in Figure (d).

FIG. 15G shows aligned multiwalled CNTs carpet grown on Poly Si/Ti 50nm/Ni 30 nm (substrate was annealed at 400° C. for 15 hours) with gasratio of H₂/C₂H₂; 155/15 at 745° C.

FIG. 15H C shows aligned multiwalled CNTs carpet grown on Poly Si/Ti 50nm/Ni 30 nm (sample was annealed at 400° C. for 15 hours) with gas ratioof Ar/NH₃/C₂H₂; 250/150/25 sccm at 745° C.

FIG. 15I shows aligned patterned CNTs grown on 30 nm Ni on 50 nm Ti onPoly-silicon (patterned sample was annealed at 400° C. for 15 hours)with gas ratio of Ar/H₂/C₂H₂; 30/125/20 sccm at 745° C.

FIG. 15J shows TEM image of multiwalled CNTs grown on 30 nm Ni onPoly-silicon with gas ratio of Ar/H₂/C₂H₂: 100/20/15 sccm at 745° C.

FIG. 15K shows TEM image of multiwalled CNTs grown on 30 nm Ni on P-typesilicon with gas ratio of Ar/H₂/C₂H₂; 100/20/15 sccm at 745° C.

FIG. 15L shows TEM image of patterned CNTs grown on 60 nm Ni on crackedPoly-silicon with gas ratio of Ar/H₂/C₂H₂; 100/20/15 at 745° C.

FIG. 15M shows TEM image of multiwalled CNTs carpet grown on Poly Si/Ti50 nm/Ni 30 nm (sample was annealed at 400° C. for 15 hours) with gasratio of Ar/H₂/C₂H₂; 100/20/15 sccm at 745°.

FIG. 16A shows a setup for thermal chemical vapor deposition.

FIG. 16B shows ACNTs grown on P-type Si with growth conditions;Ar/H₂/Temp/FePc/Time: 40/75/902/0.6/8 min.

FIG. 16C shows ACNTs grown on Quartz with growth conditions;Ar/H₂/Temp/FePc/Time: 20/20/902/0.4/20 min.

FIG. 16D shows ACNTs grown on SiOx with growth conditions;Ar/H₂/Temp/FePc/Time: 40/110/902/0.3/10 min.

FIG. 16E shows ACNTs grown on SiN with growth conditions;Ar/H₂/Temp/FePc/Time: 40/120/902/0.3/10 min.

FIG. 16F shows ACNTs grown on P-type Si with growth conditions;Ar/H₂/Temp/FePc/Time: 80/150/820/0.6/6 min.

FIG. 16G shows Chip # SP457 ACNTs grown on P-type Si with growthconditions; Ar/H₂/Temp/FePc/Time: 80/75/960/0.6/1.5 min.

FIG. 16H shows ACNTs grown on P-type Si with growth conditions;Ar/H₂/Temp/FePc/Time: 100/100/900/0.4/5 min.

FIG. 16I shows TEM image of multiwalled CNTs grown on SiOx with growthconditions; Ar/H₂/Temp/FePc/Time: 15/20/900/0.5/10 min.

FIG. 16K shows a TEM image of multiwalled CNTs grown on P-type Si withgrowth conditions; Ar/H₂/Temp/FePc/Time: 80/75/960/0.6/5 min.

FIG. 17 shows a fabrication process of catalyst insulation andmechanical support.

FIGS. 18A and 18B: (a) SEM of ACNT film before supercritical treatment;(b) TEM of ACNT before supercritical treatment.

FIG. 18C and FIG. 18D: (a) SEM of ACNT film after supercriticaltreatment; (b) TEM of ACNTs after supercritical treatment.

FIG. 18E Line scans EDX of ACNT after supercritical treatment.

FIG. 18F High resolution TEM of SWNT sample after supercriticaltreatment.

FIG. 18G Signature CV of 100 ppm 64BFA dissolved in methylene chloridesolution in presence of 0.05 M tetra butyl ammonium hexafluoro phosphatesupporting electrolyte.

FIG. 18H 0.05 M tetra butyl ammonium hexafluoro phosphate supportingelectrolyte in methylene chloride solvent. Scan rate 20 mV/s. ACNT filmelectrochemical analyses after SFT treatment.

FIG. 18I SEM characterization of ACNT sample after supercriticaltreatment with conditions 2.

FIG. 18J 0.05 M tetra butyl ammonium hexafluoro phosphate supportingelectrolyte in methylene chloride solvent, Scan rate 20 mV/s. ACNT filmelectrochemical analysis after condition 2 treatment.

FIG. 19A i-E curve for the electrolysis of 0.1 M ClO− in 0.1 M phosphatebuffer.

FIG. 19B Typical amperometric reduction curves obtained for thereduction of hypochlorous acid in 18.2 MΩ-cm water. R²=0.9888 in thiscase.

FIG. 19C Effect of conductivity (mS/cm, plot on the left) and pH vs. theconcentration of chlorine in its solutions.

FIG. 19D Plots of resulting reduction charge Vs. free chlorineconcentration using CNT electrodes (with and without the addition ofelectrolyte). For comparison, a similar plot using a commercial dopeddiamond electrode is also presented.

FIG. 19E Free chlorine Reduction Reaction: Comparison of the response ofCNTs, Diamond, Glassy Carbon and Gold. Reduction performed at constantpotential of 0 V, applied for 5 s in 0.05 M phosphate buffer.

FIG. 19F Response Precision of Free Chlorine Reduction Reaction, n=10.

FIG. 20A Typical calibration curve for the solid contact Ca-ISE (Chip#SP-97). 10⁻¹-10⁻⁵ M CaCl₂ solutions were prepared in Tris Buffer (pH7.4) and the EMF was measured against Ag/AgCl reference electrode.

FIG. 20B Doped and Undoped PANT response to Calcium. 10⁻¹-10⁻⁵ M CaCl₂solutions were prepared in Tris Buffer (pH 7.4) and the EMF was measuredagainst Ag/AgCl reference electrode.

FIG. 20C Calibration curve for the solid contact Ca-ISE (Chip # SP-158).10⁻¹-10⁻⁴ M CaCl₂ solutions were prepared in Tap H₂O and the EMF wasmeasured against Ag/AgCl reference electrode.

FIG. 20D SEM images of the prepolymerized CNT film (Chip # SP-169). a)Cross sectional view of the conducting polymer-CNT cladding. The sidewalls of the CNTs are visible and b) Top view of the structure.

FIG. 20E Selectivity studies for Ca²⁺ selective electrode (Chip ifSP-97). (▪) Response for Ca²⁺ in DI H₂O and (♦) Response for 0.01 MCaCl₂ in 10⁻¹-10⁻⁴ M KCl.

FIG. 20F Experimental time traces for the EMF measurements of thepre-polymerized PANi (Chip # SP-171).

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The present invention may be understood more readily by reference to thefollowing detailed description taken in connection with the accompanyingfigures and examples, which form a part of this disclosure. It is to beunderstood that this invention is not limited to the specific devices,methods, conditions or parameters described and/or shown herein, andthat the terminology used herein is for the purpose of describingparticular embodiments by way of example only and is not intended to belimiting of the claimed invention. Also, as used in the specificationincluding the appended claims, the singular forms “a,” “an,” and “the”include the plural, and reference to a particular numerical valueincludes at least that particular value, unless the context clearlydictates otherwise. When a range of values is expressed, anotherembodiment includes from the one particular value and/or to the otherparticular value. Similarly, when values are expressed asapproximations, by use of the antecedent “about,” it will be understoodthat the particular value forms another embodiment. All ranges areinclusive and combinable.

It is to be appreciated that certain features of the invention whichare, for clarity, described herein in the context of separateembodiments, may also be provided in combination in a single embodiment.Conversely, various features of the invention that are, for brevity,described in the context of a single embodiment, may also be providedseparately or in any subcombination. Further, reference to values statedin ranges include each and every value within that range.

The antennae assembly electrodes include an electrically conductivelayer at least partially surmounting a substrate; and an assembly ofdoped antennae vertically oriented with respect to the electricallyconductive layer. Each of the doped antennae comprises a doped MWNTcomprising: a base end attached to the electrically conductive layer, amid-section comprising an outer surface surrounding a lumen, wherein atleast a portion of the outer surface of the mid-section is capable ofbeing in fluidic contact with an environment in contact with theantennae. The doped MWNT also has a top end disposed opposite to thebase end, and a dopant attached to or contained within the lumen, adopant attached to or contained within the outer surface, a dopantattached to or contained within the top end, or any combination thereof.Sensors and field-effect transistors can be suitably fashioned usingthese antennae assembly electrodes, as described further herein.

In certain aspects of the present invention there are provide MWNT basedsensors that are composed of electrode arrays comprising aligned MWNTsthat can be electrically conductive as well as chemically inert to waterand biological media. Suitable sensors are capable of sensing one, andpreferably more than one analytes in a test fluid. Such carbon materialstructures make ideal electrochemical sensors by evoking two propertiesof electrodes; the chemical inertness of diamond with the electricalconductivity (i.e., electron mobility) of a metal. The chemicalinertness relates to the ability to measure an electro-chemical reactionwithout memory (i.e., retention) of such reaction. The graphene electronconductivity of MWNTs can range from metallic to semi-conducting whilethe surface chemistry can be controlled by varying the environmentalconditions, such as, temperature, pressure, and chemical environment.The unique properties of MWNTs allow for the adaptation to noveldetection schemes by manipulating conduction of CNTs and mediating suchcharacteristic by chemical doping.

CNT's may be grown by Chemical Vapor Deposition (CVD) into a template ofperpendicularly aligned arrays of CNT electrodes. The CNTs diameter,length and pitch is controlled by the chemical vapor deposition (“CVD”)growth process to create a spaced NT electrode array structure thatoptimizes effective electrolysis surface, yet minimizes Ohmic lossthrough the sample medium. In certain aspects, the nominally idealizedCNT nanoarray structure comprises a 10:1 pitch:diameter ratio atnanometer dimensions. Without being bound by any particular theory ofoperation, the CNT nanoarray structure of various embodiments of thepresent invention apparently minimizes analytical measurement errorsthat are otherwise present in conventional electrode structures andmaterials.

The readily achievable CNT structural design disclosed herein provides anumber of beneficial design attributes that are especially important formonitoring drinking water. The low salt content (high electricalimpedance) of drinking water presents a unique challenge toelectrochemical measurement because small variation in electrolytecontent will introduce significant measurement error. The ability tomeasure variable conductivity water samples from drinking water to seawater without analytical performance degradation is an importantcriterion of robust product technology and especially important forcontinuous monitoring.

The CNT sensors can be used in different modes to selectively detectanalytes. In one mode, the CNTs can be used as a source or depository ofelectrons to be exchanged with the medium in an electrolytic reaction.In a second mode, the CNTs can be used to function as a static electricfield measurement in the potentiometric mode (i.e, zero current flow.)In some embodiments, CNT sensors can be used in continuous electrolyticmonitoring of strong oxidants (such as chlorine) in drinking water.

Without being bound to a particular theory of operation, the CNT sensorsare particularly well-suited for use in strong oxidants because of thehigh chemical resistance of CNTs. In electrochemical terms, the CNTssurface chemistry is essentially unaffected by chlorine in the presenceor absence of electrolysis. This is characteristically unlike noblemetal electrodes (e.g., Pt or Au) in which the surface can indeed beoxidized or electrolytically altered. This property allows for a broadoperating voltage window for measuring electro-active molecules in waterusing various embodiments of the CNT-based sensors of the presentinvention. CNT working electrodes operating in the electrolyticmeasurement mode do not necessarily require coatings or dopants toeffect selective measurement. In one embodiment, specificity andsensitivity of redox response is essentially enhanced by voltage (i.e.,bias) programming techniques. Molecules with redox potentials that falloutside the operating voltage window can be mediated by dopants to shiftthe energy (i.e., voltage) to within the operating voltage window.Programming techniques are provided in U.S. Pat. No. 5,120,421 to Glasset al., “Electrochemical sensor/detector system and method”, the portionof which pertaining to programming is incorporated by reference herein.

In the potentiometric mode, the CNTs can measure static electric fieldsgenerated by ion charge accumulation. In these embodiments, the CNTs canbe doped with selective ligand molecules that selectively bind ions.Such a CNT ion sensor can be employed to detect calcium ion content indrinking water as a measure of water hardness. In this mode, and withoutbeing bound by any particular theory of operation, the electricalconductivity of CNTs tends to be irrelevant to the measurement and theCNT appears to function as a conduit for the measure of static charge.In this mode, the dopant chemistry evokes selective chemical responsewhich appears to be manifested as a chemical potential or voltage sensedby the CNT.

Doping of CNTs can be accomplished in several ways, i.e., by; “peapod”formation (e.g., nanotubes containing other atoms, molecules, or bothresiding within the interior of the nanotube), polymer filmcoatings/claddings of CNTs, and by chemical linkage to the graphenecarbon of the CNT and/or linkage to the cladding. Further details onforming CNT peapods can be found in U.S. Pat. No. 6,863,857, “Hybridmaterials and methods for producing the same” to Luzzi and Smith, theportion of which pertaining to the formation of filled CNTs isincorporated by reference herein. A doping embodiment can becharacterized by a peapod structure created by one or more activereagents (or dopants) to a CNT lumen and annealing the CNT toencapsulate the active reagents or dopants. Without being bound by anyparticular theory of operation, this provides a cocoon-like CNTprotection of active reagent or dopant while providing electron exchange(i.e., tunneling) between the interior dopant and the outside medium.The graphene carbons of the CNTs are believed to function as a conduitfor electron transfer between the oxidation state of the sample moleculeand the measurement circuit. The peapod electrolysis current is ameasure of the rate of electron transfer incurred by the sample andmediated by dopant. In embodiments when the dopant is an ionophore, ioncharge accumulation on the CNT can be manifested as a voltage that isrelated thermodynamically to the electrolyte solution chemicalpotential. Large binding constants of ion-ligand complex formationfavors the partitioning of charge to the interior of the filled MWNT andthe electric field generated is in equilibrium with sample ion content.

Another way to dope the MWNTs is to use electrospray ionization, whichcan selectively deposit dopants in, or on, particular MWNTs on theelectrode. Details of selective doping of particular nanotubes onantennae assembly electrodes using electrospray are provided in U.S.Provisional Patent Application Ser. No. 60/762,613, “ElectrosprayDeposition: Devices and Methods Thereof”, by Salvatore Pace and FrancisMan, filed Jan. 26, 2006, the entirety of which is incorporated byreference herein.

In certain embodiments, doped polymeric claddings that coat the CNT(i.e., graphene) backbone may be formed by free radical polymerizationfrom organic monomers. Free radical polymerization may be mediated by anumber of methods know in the art, including RF plasma reaction (i.e.,in the gas phase), by electrolytic polymerization (i.e., in the liquidphase), or any combination thereof. One scheme for polymer impregationis accomplished by trapping dopant coincident with the polymerization ina co-deposition process. Alternatively, a polymer CNT cladding can beimpregnated by phase transfer partitioning, for example, by usingsupercritical fluid carbon dioxide (“scCO₂”) as a partitioning solvent.Stable CNT interfacial boundaries can be created using a selectivereagent that chemically links to the CNT backbone as a precursor step topolymer coating (i.e., cladding). In one embodiment, combining a peapodstructure with an exterior CNT coating gives rise to unique reagentinteractions depicted by the interplay of sample modulatedelectro-chemiluminescent (ECL) emission (e.g., Example #6). An ammoniasensor (e.g., Example #3) is another example of the interplay betweenthe gas barrier PTFE cladding and a nonactin-doped peapod CNT.

The present invention relates to the design and methods of fabricationof MWNT chemical and biological sensors and their use thereof. MWNTs canbe chemically doped with reagents to respond electro-chemically and/orphoto-chemically to specifically targeted molecules in water samples andbiological media. Devices and methods of detection are also providedthat measure the transduction of chemical to electrical or chemical tophotonic signals. These signal can be electronically processed to yieldhigh sensitivity and specificity responses to a variety of analyticallytargeted molecules.

In one mode, the subject invention includes a plurality of CNT sensingelements patterned on a silicon chip. Each CNT sensing element comprisesa plurality of substantially aligned MWNTs grown perpendicularly to theplane of the substrate (Si) and subject to contact or exposure to testsample fluid. Additional circuit elements may also be mounted on thesubstrate (e.g., a silicon chi, such as electrical conduits, terminationpoints and amplifiers, photon sources, and other components. CNT growthcan be generated by chemical vapor deposition (CVD) and the geometricpatterns defined by the electron-beam lithography of the metal catalyst.The CVD grown CNT array patterns can be perpendicularly aligned and inelectrical contact with the metal. In one embodiment, a suitable CNTsensing element includes a silicon chip comprising a combination ofelectrochemical sensing elements based on redox electrolysis and chargecoupled ion transduction. A combination of these elements comprise amulti-sensor chemical profiling chip. An example of a nominal drinkingwater test combination of free and total chlorine and water hardnesswould deploy the following sensors: CNT-gated FET for calcium, a CNTWorking electrode for free chlorine and a doped/cladded CNT peapodworking electrode-photodiode combination for tot-Cl₂ modulatedelectro-chemiluminescence.

CNT sensor elements can be fabricated with processes known to those ofskill in the art of semiconductor materials and processing. Each CNTsensor element can be doped with selective reagent to impart chemicaldetection specificity. In one embodiment, for example, an ensemble ofCNT sensor elements can be operated in concert to effect the chemicalprofiling of drinking water. In other embodiments, undoped CNTs can bevoltage programmed to elicit selective responses for electro-activemolecules such as chlorine and chloramines. Redox mediators such asRu(bpy) can be electrolytically activated to generate photon emissionthat can also be modulated by sample interaction. In the potentiometricmode (charge coupling), CNTs can be doped with ionophores thatselectively react with sample target ions. A combination of CNT sensorelements can therefore be selected to detect for a drinking water“disinfection profile” as outlined in Table I. The CNT sensor elementsof the present invention provide a broad electrolysis operating windowfor water samples and also virtually eliminate artifacts such as iontransport partitioning and non-specific ion exchange at sample/membraneinterfaces that diminish the ion detection (sensitivity) limit ofconventional ion selective electrode (ISE) sensors.

Redox Detection-Electrolytic Sensing:

In another mode, a CNT sensor element is provided that can be operatedin an electrolytic measurement mode. In this mode, the CNT sensorelement does not chemically participate in the electrolysis, rather itfunctions as an inert working electrode surface to conduct electrolysisof electro-active molecules. This property allows the CNTs to measureelectrolytic currents with little or no inter-sample surface memoryeffects that would otherwise compromise precision and accuracy. Dopedmediators can also be suitably used to facilitate the electron transferat the CNT to enhance the kinetics of electron transfer, to lower theenergy (voltage) required for the measurement, or both. Mediatedelectron transfer suitably allows for electrolytic measurement in auseful voltage region.

Suitable redox mediators can be electrolytically activated to excitedstates resulting in photon emission as they dismutate to the groundstate. Such transitions can be electrochemically initiated at the CNTworking electrode and modulated by suitable redox active sample targetmolecules. In certain embodiments, analytes such as mono-chloroamine canbe chemically oxidized by Ru(bipy)2+ dopant to Ru(bipy)3+ whileRu(bipy)3+ can be electrolytically reduced to the Ru(bipy)2+. Theinteraction between the Ru oxidized species within the cladding and thepeapod (e.g., the reduced species) generates photon emission at 610 nmwhich is, in turn, modulated by the sample. Without being bound by anyparticular theory of operation, electrolysis at the CNT surface triggersthe electro-chemiluminescence (“ECL”) although the modulation ischemically induced by a sample oxidant, such as chloramines. Hence, fordrinking water samples, the emission intensity can be used to measuretotal chlorine.

Ion & Gas Detection-Potentiometric Sensing:

The potentiometric (ISE) sensor (voltage measurement at zero current)can measure CNT charge accumulation (i.e., electric field), as aconsequence of ionic charge buildup on the CNTs. The CNTs can be dopedwith suitable ionophores (e.g., cyclic polyethers) to induce a selectiveion response of a test water sample. Various suitable ionophores can beused as described herein. Without being bound by any particular theoryof operation, the ionophores function as a specific binding agent forthe ion. Accordingly, the accumulation of charge on the CNT can bemeasured with an electrometer amplifier circuit. The CNTs function as ananofield of antennas that receive the modulating ion charge that, inturn, measures a chemical potential (i.e., voltage).

The CNT sensor elements can be electronically passive (i.e., noamplifier). In other modes, the ISE structure can combine one or moreCNT sensor elements with an active circuit such as a field effecttransistor (FET). For example, the CNT's can be CVD grown and patterneddirectly on a gate surface of a suitable FET. Suitable FETs can have agate that is ion specifically modulated by the sample solution/ionophoreinteraction. The modulated ion response (or chemical potential) is tunedby the ionophore CNT-dopant chemistry. In a further embodiment,integrating amplifiers to sensors on a substrate chip can be used toimprove signal/noise characteristic signal performance

Multi-Sensor CNT Array:

A multi-sensor CNT array can be patterned on a silicon substrate andsubsequently doped with a plurality of selective reagent to evokespecific response to a plurality of sample target molecules. Each CNTfeature can be modified to detect a single chemical species in a sample,such as drinking water. A portion of the sensing elements of themulti-sensor CNT array can comprise unmodified CNTs to measureelectrolysis currents at appropriate bias voltages corresponding to theelectro-active species. In this embodiment, select voltage programs canbe used to measure test species. Other sensing elements can be doped(chemically altered) with ionophoric or redox mediating species tomeasure surface potentials based on accumulated ion charge or redoxratio of electro-active molecules.

Among the various sensor embodiments described herein, the CNTs can bein contact with a catalytic metal surface that is patterned on a siliconsubstrate which is provided as an integral circuit component of anelectrode ensemble. This ensemble comprises an array of sensors deployedto contiguously and selectively measure a plurality of test analytes. Incertain embodiments, the device also includes one or more counter andreference electrode elements that are integrated onto the chipstructure. Such electrode elements can be strategically positioned onthe sensor to provide electrochemical support function but do notnecessarily partake in the selective sensing/response process.

EXAMPLES AND OTHER ILLUSTRATIVE EMBODIMENTS AND DESCRIPTION Silicon ChipDesign and Process Schemes for Aligned CNT Patterns I. CNT Array WorkingElectrode Pattern, FIG. [1], CNT Array Working Electrode Structure forElectrolytic Cell Configuration.

Process Description.

Referring to the sequence of process steps in FIG. 9, the process startswith a 100 mm silicon wafer substrate (902) with a 500 nm thermal oxidelayer (904) on top (steps 1 and 2). The patterning of TiW/Mo/TiWelectrically conductive layer (906) is performed in a two-steplithography process. In the first step, a liftoff resist is spin coated,and baked. In the second step, a conventional photo-resist is spincoated, exposed, and developed. During resist development, the developernot only removes the exposed photo-resist, it also removes and undercutsthe liftoff resist such that when the wafer is immersed in acetone, thesubsequent metal stack is lift off leaving a clean metal definition.Then a stack layer of TiW/Mo/TiW: 40 nm/40 nm/40 nm (b) is sputtered,followed by a reactive sputtering of 15 nm TiN (b). The metal stack(step 3) is then liftoff by immersing in acetone. Afterwards, aconventional liftoff process is performed where photo-resist ispatterned to define the gold metal contact pad (908) with a Cr adhesionlayer, followed by evaporation of a 50 nm of gold, and immersion inacetone liftoff solution (step 4). Similarly, the 7 nm nickel catalystlayer (d) is patterned by liftoff process using the liftoff resist toproduce a sharp nickel metal interface. Next, a 500 nm layer of PECVDsilicon nitride protective layer (910) is deposited at 380 C (step 5).Contact holes (912) are patterned and etched in reactive ion etching(914) (step 6). After that, the wafer is ready for MWNT (916) growthwhere substrate (902) is exposed to acetylene and ammonia gas at 400° C.(step7), followed by further chemical functionalization (918) (step 8)to give rise to a doped CNT array working electrode (900).

Process Flow

Starting Wafer

-   -   p-type boron doped 100 mm silicon wafer, single side polished

Thermal Oxide Deposition

-   -   500 nm thermal oxide at 1000 C for 30 mins

Lithography 1—Interconnect

-   -   Spin LOR-5a 40H rpm for 10 sec    -   Softbake on hot plate for 5 mins at 180 C    -   Spin 220 4 k rpm for 10 sec    -   Softbake on hot plate for 90 s at 115 C    -   Expose 5 sec at 25.0 mW/cm2    -   Post-exposure bake on hot plate for 90 s at 115 C    -   Develop in MIF 300 for 2 mins    -   Rinse 2 mins in DI, spin dry

TiW/Mo/TiW/TiN Interconnect Deposition

-   -   Sputter 40:40:40 nm of TiW/Mo/TiW onto wafer    -   Sputter 15 nm of Ti under nitrogen environment    -   Liftoff in acetone    -   Rinse 2 mins DI, spin dry

Lithography 2—Contact Pad

-   -   Spin HMDS 4 k rpm for 30s    -   Spin 220 4 k rpm for 10 sec    -   Softbake on hot plate for 90 s at 115 C    -   Expose 5 sec at 25.0 mW/cm2    -   Post-exposure bake on hot plate for 90 s at 115 C    -   Develop in MIF 300 for 2 mins    -   Rinse 2 mins in DI, spin dry

Gold Metal Pad Deposition

-   -   Evaporate 10:100 nm of Cr/Au onto wafer    -   Liftoff in acetone    -   Rinse 2 mins DI, spin dry

Lithography 3—Catalyst Deposition

-   -   Spin LOR-5a 40H rpm for 10 sec    -   Softbake on hot plate for 5 mins at 180 C    -   Spin 220 4 k rpm for 10 sec    -   Softbake on hot plate for 90 s at 115 C    -   Expose 5 sec at 25.0 mW/cm2    -   Post-exposure bake on hot plate for 90 s at 115 C    -   Develop in MIF 300 for 2 mins    -   Rinse 2 mins in DI, spin dry

Nickel Catalyst Deposition

-   -   Evaporate 7 nm of nickel onto wafer    -   Liftoff in acetone    -   Rinse 2 mins DI, spin dry

Passivation Nitride Deposition

-   -   PECVD deposit 500 nm of silicon nitride at 380 C

Lithography 4—Contact Opening

-   -   Spin HMDS 4 k rpm for 30 s    -   Spin 220 4 k rpm for 10 sec    -   Softbake on hot plate for 90 s at 115 C    -   Expose 5 sec at 25.0 mW/cm2    -   Post-exposure bake on hot plate for 90 s at 115 C    -   Develop in MIF 300 for 2 mins    -   Rinse 2 mins in DI, spin dry

Passivation Nitride Etch

-   -   Plasma etch, P=100 W, P=100 mT, CF4=40 sccm, O2=1 sccm MWNT Grow        (by the PECVD-Acetylene method or the thermal CVD growth        method; A. gas phase, B. solid precursor)    -   PECVD Acetylene: ammonia=54 sccm:200 sccm, P=5 mBar, T=675 C. or        Thermal CNT growth (as outlined below)

II. CNT-Gated MOSFET Pattern; FIG. [2]; CNT-Gated MOSFET Structure forIon Detection

Process Description.

Referring to the sequence of process steps in FIGS. 10 a-10 r, thestarting material is a p-type silicon wafer (1002) with a 40 nm thickpad dioxide (1004) (FIG. 10 a). A 200 nm thick LPCVD silicon nitride(1006) is then deposited at 820 C (FIG. 10 b). The nitride and pad oxidelayer are patterned by conventional photo-resist, and etched in reactiveion etching followed by a 250 nm silicon recess etch (1008) (FIG. 10 c).A dose of 5e13/cm2 boron (1010) is implanted at 60 kev to form the fieldimplanation (FIG. 10 d). After that, a 700 nm thick silicon dioxide(1014) is grown in the field area (1012) (FIG. 10 e). Next, the nitrideand pad oxide (1004, 1006) are stripped off by immersing into hotphosphoric acid and buffered hydrofluoric acid (FIG. 10 f). Asacrificial gate oxide (1016) is grown at 1000 C, followed by apolysilicon (1018) deposition at 625 C (FIG. 10 g). A conventionalphoto-resist is applied to define the source and drain areas (1020) ofthe transistor. Next, exposed polysilicon layer is etched using reactiveion etching and sacrificial gate oxide is wet etched (FIG. 10 h). Afterthat, a dose of phosphorus ion (1040) is implanted, followed by adrive-in (FIG. 10 i). Subsequently, the polysilicon (1018) and oxidelayer (1016) are sacrificially removed (FIG. 10 j). Then another gateoxide (1022) is grown (FIG. 10 k) and a 30 nm catalyst nickel layer(1024) is sputtered (FIG. 10 l). Conventional photoresist is then usedto define the source and claim 1026) of each gate (1022) of thetransistor where nickel (1024) and gate oxide (1022) is etched (FIG. 10m). A thin 200 nm of plasma-enhanced chemical vapor deposition (PECVD)silicon nitride is then deposited at 380 C to form the passivation layer(1028) (FIG. 10 n). The nitride is subsequently patterned and etched todefine the contact holes (1030) to the source and drain (1026) and toreveal the CNT growth area (1032) (FIG. 10 o). Photoresist (not shown)is next patterned and a 100 nm thick gold is then evaporated, andsubsequently lift off to form metal contact (1034) (FIG. 10 p). Thewafer (1036) is then exposed to acetylene and ammonia gas at 400 C (FIG.10 q) in a PECVD chamber where vertically aligned MWNTs (1038) are grownon the exposed nickel (1024). After that, the nanotubes are ready forchemical functionalization (doping) (FIG. 10 r) with a dopant (1042).

Process Flow

Starting Wafer

-   -   p-type boron doped 1.2 ohm-cm, 100 mm silicon wafer <100>,        single side polished

Grow Pad Oxide

-   -   Standard Prefurance cleaning—rinse to 15.2 M ohm-cm    -   Grow 40 nm of silicon dioxide: T_(dep)=22 min, dry O₂, 1000 C,        40 nm thick    -   Anneal 10 min in N₂

LPCVD Nitride Deposition

-   -   Deposit 200 nm of LPCVD nitride: 820 C, Tdep=40 min

Lithography 1: Active Area

-   -   Spin HMDS 4 k rpm for 30 s    -   Spin 220 4 k rpm for 10 sec    -   Softbake on hot plate for 90 s at 115 C    -   Expose 5 sec at 25.0 mW/cm2    -   Post-exposure bake on hot plate for 90 s at 115 C    -   Develop in MIF 300 for 2 mins    -   Rinse 2 mins in DI, spin dry

Nitride Etch

-   -   Descum: O₂, 20 W, 300 mT, 1 min    -   Reactive Ion Etch: CF₄:20 sccm, O₂:1 sccm 100 mTorr, 100 W, 34        min

Pad Oxide Etch

-   -   Reactive Ion Etch: CHF₃=25 sccm, CF₄=25 sccm, P=183 W, P=40 mT,

Si Recess Etch

-   -   Wet etch in NH₄F:H₂O:HNO₃=3; 33:64 by volume, T_(etch)=4 mins    -   Rinse 2 mins in DI, spin dry

Field Implant

-   -   Boron, 5e13/cm², 60 kev

Strip Resist

-   -   PRS-2000, 15 min, 100° C.    -   Acetone 3 mins    -   Propanol 3 mins    -   Rinse 5 mins in DI, spin dry

Field Oxidation

-   -   Standard prefurance clean    -   Grow 680 nm of silicon dioxide: O₂, T_(dep)=dry 5 mins/wet 70        mins/dry 5 mins,    -   1100° C.    -   Anneal 10 min in N₂

Oxynitride Strip

-   -   Wet etch in BHF for 15 sec    -   Rinse 5 mins in DI, spin dry

Strip Nitride

-   -   Wet etch in hot phosphoric acid for 30 mins at 160° C.

Pad Oxide Etch

-   -   Wet etch in BHF for 45 sec    -   Rinse 5 mins in DI, spin dry

Sacrificial Gate Oxide Growth

-   -   Standard prefurance clean    -   Grow 40 nm of silicon dioxide: dry O₂, T_(dep)=22 mins, 1000° C.    -   Anneal 10 min in N₂

Polysilicon Deposition

-   -   Deposit 52 nm of LPCVD nitride: 625 C, Tdep=52 min

Lithography 2: Poly

-   -   Spin HMDS 4 k rpm for 30 s    -   Spin 220 4 k rpm for 10 sec    -   Softbake on hot plate for 90 s at 115 C    -   Expose 5 sec at 25.0 mW/cm2    -   Post-exposure bake on hot plate for 90 s at 115 C    -   Develop in MIF 300 for 2 mins    -   Rinse 2 mins in DI, spin dry

Polysilicon Etch

-   -   RIE etch of 52 nm of polysilicon, P=65 W, P=5 mT, SF₆=20 sccm,        O₂=3 sccm

Strip Resist

-   -   PRS-2000, 15 min, 100° C.    -   Acetone 3 mins    -   Propanol 3 mins    -   Rinse 5 mins in DI, spin dry

Source/Drain Oxide Etch

-   -   Unmasked    -   Wet etch in buffered HF for 45 sec    -   Rinse 5 mins in DI, spin dry,

Source/Drain Predep

-   -   Standard Prefurance clean with HF dip    -   Phosphorus diffusion: POCl₂: 450 sccm, O₂: 150 sccm, 950° C., 20        mins

Source Drain Drive-in

-   -   Grow 140 nm of silicon dioxide: O₂, T_(dep)==dry 5 mins/wet 15        mins/dry 5 mins,    -   950° C.    -   Anneal 10 min in N₂

Strip Polysilicon

-   -   Wet etch in NH₄F:H₂O:HNO₃=3;33:64 by volume, T_(etch)=4 mins    -   Rinse 2 mins in DI, spin dry

Strip Sacrificial Gat Oxide

-   -   Wet etch in buffered HF for 45 sec.    -   Rinse 2 mins in DI, spin dry

Gate Oxide Growth

-   -   Standard prefurance clean    -   Grow 40 nm of silicon dioxide: dry O₂, T_(dep)=22 mins, 1000° C.    -   Anneal 10 min in N₂

Nickel Catalyst Deposition

-   -   Evaporate 7 nm of nickel onto wafer

Lithography 2: Poly

-   -   Spin HMDS 4 k rpm for 30 s    -   Spin 220 4 k rpm for 10 sec    -   Softbake on hot plate for 90 s at 115 C    -   Expose 5 sec at 25.0 mW/cm2    -   Post-exposure bake on hot plate for 90 s at 115 C    -   Develop in MIF 300 for 2 mins    -   Rinse 2 mins in DI, spin dry

Nickel Etch

Gate Oxide Etch

-   -   Wet etch in buffered HF for 45 sec    -   Rinse 2 mins in DI, spin dry

Passivation Nitride Deposition

-   -   PECVD deposit 500 nm of silicon nitride at 380 C

Lithography 4—Contact Opening

-   -   Spin HMDS 4 k rpm for 30 s    -   Spin 220 4 k rpm for 10 sec    -   Softbake on hot plate for 90 s at 115 C    -   Expose 5 sec at 25.0 mW/cm2    -   Post-exposure bake on hot plate for 90 s at 115 C    -   Develop in MIF 300 for 2 mins    -   Rinse 2 mins in DI, spin dry

Passivation Nitride Etch

Plasma etch, P=100 W, P=100 mT, CF4=40 sccm, O2-1 sccm

MWNT Grow

-   -   PECVD Acetylene: ammonia=54 sccm:200 sccm, P=5 mBar, T=675 C.        III. CNT Islands Pattern; FIG. 131 CNT Patterned Islands. This        CNT Pattern and Process is Representative of a Multisensor Chip        Design.

Process Description.

A process for forming a doped CNT assembly electrode array having CNTpatterned islands is illustrated in FIG. 11. The process starts with a100 mm silicon wafer substrate (1102) with a 500 nm thermal oxide layer(1104) on top (step1). The patterning of electrically conductive layer(1106) is performed in a two-step lithography process. In the firststep, a liftoff resist is spin coated, and baked. In the second step, aconventional photo-resist is spin coated, exposed, and developed. Duringresist development, the developer not only removes the exposedphoto-resist, it also removes and undercuts the liftoff resist such thatwhen the wafer is immersed in acetone, the subsequent metal stack islift off leaving a clean metal definition. Then a stack layer ofTiW/Mo/TiW: 40 nm/40 nm/40 nm is sputtered, followed by a reactivesputtering of 15 nm TiN to yield the electrically conductive layer(1106). The metal stack is then liftoff by immersing in acetone. Afterthat, a conventional liftoff process is performed where photo-resist ispatterned to define the gold contact pad, followed by evaporation of a50 nm of gold metal (1108), and immersion in acetone liftoff solution.Similarly, the 7 nm nickel catalyst layer (not shown) is patterned byliftoff process using the liftoff resist to produce a sharp nickel metalinterface (step 4). Next, a 500 nm layer of PECVD silicon nitridepassivation layer (1110) is deposited at 380 C (step 5). Contact holesare patterned to expose the metal contact pads (1108) by e-beamlithography and etched in reactive ion etching (step 6). After that, thewafer is ready for MWNT (1116) growth (f) where wafer is exposed toacetylene and ammonia gas at 400 C (step8), followed by further chemicalfunctionalization (g) (step g) to dope the MWNTs (not shown).

Process Flow

Starting Wafer

-   -   p-type boron doped 100 mm silicon wafer, single side polished

Thermal oxide Deposition

-   -   500 nm thermal oxide at 1000 C for 30 mins

Lithography 1—Interconnect

-   -   Spin LOR-5a 4011 rpm for 10 sec    -   Softbake on hot plate for 5 mins at 180 C    -   Spin 220 4 k rpm for 10 sec    -   Softbake on hot plate for 90 s at 115 C    -   Expose 5 sec at 25.0 mW/cm2    -   Post-exposure bake on hot plate for 90 s at 115 C    -   Develop in MIF 300 for 2 mins    -   Rinse 2 mins in DI, spin dry

TiW/Mo/TiW/TiN Interconnect Deposition

-   -   Sputter 40:40:40 nm of TiW/Mo/TiW onto wafer    -   Sputter 15 nm of Ti under nitrogen environment    -   Liftoff in acetone    -   Rinse 2 mins DI, spin dry

Lithography 2—Contact Pad

-   -   Spin HMDS 4 k rpm for 30 s    -   Spin 220 4 k rpm for 10 sec    -   Softbake on hot plate for 90 s at 115 C    -   Expose 5 sec at 25.0 mW/cm2    -   Post-exposure bake on hot plate for 90 s at 115 C    -   Develop in MIF 300 for 2 mins    -   Rinse 2 mins in DI, spin dry

Gold Metal Pad Deposition

-   -   Evaporate 10:100 nm of Cr/Au onto wafer    -   Liftoff in acetone    -   Rinse 2 mins DI, spin dry

Lithography 3—Catalyst Deposition

-   -   Spin LOR-5a 4011 rpm for 10 sec    -   Softbake on hot plate for 5 mins at 180 C    -   Spin 220 4 k rpm for 10 sec    -   Softbake on hot plate for 90 s at 115 C    -   Expose 5 sec at 25.0 mW/cm2    -   Post-exposure bake on hot plate for 90 s at 115 C    -   Develop in MIF 300 for 2 mins    -   Rinse 2 mins in DI, spin dry

Nickel Catalyst Deposition

-   -   Evaporate 7 nm of nickel onto wafer    -   Liftoff in acetone    -   Rinse 2 mins DI, spin dry

Passivation Nitride Deposition

-   -   PECVD deposit 500 nm of silicon nitride at 380 C

Lithography 4—Contact Opening

-   -   Spin HMDS 2 k rpm for 20 s    -   Spin 950K-A25 k rpm for 45 sec    -   Softbake on hot plate for 30 mins at 180 C    -   Expose 1000 pAs/cm at 30 kv    -   Post-exposure bake on hot plate for 2 mins at 100 C    -   Develop in 1:3MIBK:IPA for 2 mins    -   Rinse 2 mins in DI, spin dry

Passivation Nitride Etch

-   -   Plasma etch, P=100 W, P=100 mT, CF4=40 sccm, O2=1 sccm

MWNT Grow

-   -   PECVD Acetylene: ammonia=54 sccm:200 sccm, P=5 mBar, T=675 C.

III. Integrated Multi-Sensor Pattern:

FIG. [4] depicts a plan view of a four sensor chip lay-out comprisingtwo electrolytic cell Sensor Structures and two CNT-gated MOSFETs. Inthis four sensor chip design one reference electrode (“Ref El”) servicesthe FETs and the other Ref El and counter electrode is combined with thetwo CNT Working electrodes.

Fabrication Process (Multi-sensor Chip)

The fabrication process comprises a combination of steps as describedabove for patterning CNT islands and FET structures. FIG. 5 is aschematic illustration of a cladded CNT peapod used in variousembodiments of the present invention. CNTs can be chemically doped fromwithin and outside the graphene wall. Suitable polymer claddings maycomprise a variety of functional groups, i.e., conductive and insulatingpolymers, donor/acceptor semi-conducting polymers, redox activepolymers, or any combination thereof. The peapod or cladding can also bedoped with ionophores for the specific detection of ions in certainembodiments. Referring to FIG. 5, the cladded CNT peapod structureincludes both a polymer outer coating as well as an internal reagent.This is a generic approach to chemically doped CNTs that augments thedirect chemical and structural modification of the graphene wall itself.Polymers claddings may comprise of a variety of chemical functionality,i.e., conductive polymers, donor/acceptor semi-conducting polymers andredox active polymers. The CNT may be altered in p or n character, maybe functionalized with reactive molecules, or any combination thereof.

FIG. 6 is a representative set of chemical compounds and polymers thatform the CNT claddings and peapods. Suitable dopant materials forcladded-peapod CNTs include ionophore charge carriers, redox polymers,ion exchangers, conductive polymers, and any combination thereof. The18-Crown-6 polyether dopant is selective ligand for cations. Cryptands,calyxarenes and open chain polyethers are better ionophore performers asare the naturally occurring antibiotics, examples of which includevalinomycin, monensin, and nonactin. Examples of conductive polymersare; electronic conduction redox polymers, ionic conduction ion-exchangepolymers and electron donor/acceptor co-polymers. CNT electrolysismediation may occur by direct exchange of electrons between the redoxpolymer and the solution phase species, or indirectly by modulation ofthe donor/acceptor conductivity or ion exchange rate, or both.

FIG. 7 provides illustrations of representative donor-acceptor polymerchemistries for CNT cladding dopants. These dopants modify the p-ncharacter of CNTs using one or more polymer coatings. Donor-acceptorpolymer dopants are particularly useful as p-n character modifiers ofCNTs and are preferred over the use of metal impurity dopants.Donor-acceptor polymer dopants are can be readily synthesized free ofimpurities. Donor-acceptor polymer dopants are readily applied ascladdings on the CNTs using RF plasma polymerization that is well knownin the art. Tetracyano quinine (“TCNQ”) and iodine are representativeelectron acceptors for the polymers described.

FIGS. 8A and 8B provide schematic illustrations of a calcium ionselective sensor and an ammonia sensor. These sensors are charge coupleddevices based on a FET design using peapod CNTs and cladded peapod CNTs.In FIG. 8B, the cladding can be PTFE which functions as a gas permeablebarrier and the ionophore is selective to ammonium ion in the peapod.This is specific for ammonia gas because of the gas barrier andspecificity for NH₄ ⁺. A comparable structure for carbon dioxide gaswould employ pH ionophore in the peapod for specific CO₂ gas detection.A variety of other CNT-based sensor elements can be provided accordingto these design principles.

Suitable cladding includes any material that can function as a gaspermeable barrier. Examples of suitable cladding materials includepolymers, such as polytetrafluoroethylene (“PTFE”), and sol-gel ceramicmaterials, polymer/sol-gel hybrid materials, and any combinationthereof. In this example, the 16-Crown-6 ether ionophore is selective toammonium ion in the CNT peapod. This combination of cladding and peapodCNT is specific for ammonia gas because of the PTFE gas barrier and thespecificity of the 16-Crown-6 ether ionophore for NH₄ ⁴⁺. A comparablestructure for detecting carbon dioxide gas could employ a pH-specificionophore in the peapod to detect pH change in response to CO₂permeation into the peapod.

MWNTs Structure and Chemistry of Dopants.

A MWNT (CNT) sensing device is provided that selectively responds tosample chemical composition at the molecular level. The CNTs can befunctionalized and/or chemically doped with selective chemical agentsthat respond to chemical or electrical signals. In some embodiments thedoping modifies the electrical conduction properties of the CNT and inother embodiments, chemical receptor sites can be constructed to elicitspecific response. In one example, the CNT is polymer coated and dopedwith ionophore so that the CNT accumulates ionic charge. The charge isthen measured by capacitive coupling to an electronic device such as atransistor.

Certain embodiments exploit the unique electrical, structural andchemical properties of CNTs to create sensing elements that function atthe molecular level. Without being bound by any particular theory ofoperation, doped CNT array sensors may be viewed as nanoantennas thatcan transmit or receive electrical signals from its environment. Assuch, the antennas can be modified to react with chemical specificity,and such modification is depicted as the polymer-cladded CNT peapod onFIG. (7). Combinations of peapod structure (Luzzi patent) and claddingstructure and CNT surface functionalization can be structured to createchemically specific molecular level responsive antennas.

CNTs can be doped to behave as semiconductors varying in electricalconductivity from “metal-like” to virtual insulators. The graphene canbe modified or doped to effect dramatic changes in the electron transferor propagation by attaching electron withdrawing groups on its surface(DS. Soane, Polymers in Microelectronics, Elsevier (1989)).Donor-acceptor polymer dopants influence CNT transconductance, or redoxfunctionalized polymeric agents can mediate electron transfer across thegraphene structure/solution interface. Doping chemistry to effect p/nsemi-conducting character of CNTs is shown by FIGS. 9&10.

Ionophore CNT dopants can specifically interact with one or more ions insolution and electronically measured with a CNT gated FET. Redoxreactive molecules also can include dopants that mediate current flow inan electrochemical cell device. One embodiment is described below todetect chlorine in drinking water. Other embodiments can detect ions orredox molecules that are coupled to enzymes (suitable enzymes aredisclosed in SP Colowik, et. al., “Methods in Enzymology”, Vol. XLVI, K.Mosbach Ed., (1976)), antibodies (suitable antibodies are disclosed inM. Z. Atassi, et. al., “molecular Immunology”, Dekker, N.Y., (1984)),and DNA functionality (suitable DNA functionality is disclosed in L.Snyder, et. al., Molecular Genetics of Bacteria”, ASM Press, WashingtonD.C., (1997)) to achieve biochemical specificity and sensitivity forsuch cladded-CNT peapod “antennas”.

Suitable CNTs can vary in diameter from approximately 1 nanometer to 10nanometers or more. CNTs may be as short as a fullerene sphere structureor as long as a few micrometers (Ajayan Review article). CNTs can begrown perpendiculary on surfaces (e.g., Si) to create densely packed,aligned NTs (or arrays) or patterned as arrays of aligned CNTs withspace apart relationship templated by nanofabrication methods (e.g.,E-beam lithography and plasma etching). The array pitch is controlled byE-beam lithography so that the final structure is of fixed CNTsdiameter, length, and spacing. Random spacing is achieved by sputteringcatalyst and is a useful process when precise pitch is not required bythe design.

CNTs can be grown by chemical vapor deposition on templated catalyticsurfaces to control CNT chemistry and structure uniformity, particularlyfor aligned CNT array arrays. Such arrays function and independentnanoelectrodes in electrolytic cells to function as nearly ideal (highcurrent density/efficiency) electrodes that can be unencumbered bysolution medium measurement artifacts such as Ohmic loss caused tosolution resistance. Without being bound by any particular theory ofoperation, this property of CNT electrodes allows accurate currentmeasurement in water samples which conductivity can vary dramatically inelectrolytes content from drinking water (no salt/high electricalresistance) to sea water (with high salt content/no resistance). This isaccomplished without manipulation of sample composition, a usefulcharacteristic of sensors applied to continuous monitoring.

CVD growth process can generate a distribution of CNT's structuresrelative to graphene chirality and tube lumens. The tubes can exist assingle wall nano tubes (“SWNTs”) or multi wall nano tubes (“MWNT's”).SWNTs work best as transconductance channels for FET structures and canbe deployed as voltage gated, chemically gated devices, or both. Withoutbeing bound by any particular theory of operation, MWNT make bettercladded CNT electrodes because the inner graphene wall structure ispreserved and less likely to be impeded by the polymer coating. Theouter graphene wall can be chemically altered by functionalization andnot interfere with the inner graphene electrical properties. Althoughliterature has focused on SWNT channel FET, practical voltage gatedpoly-I-FET may function best with polymer cladded MWNTs. Peapod sensingstructures can be either SWNTs or MWNTs. When both the cladding and theCNT peapods can be doped MWNT's, the electrochemical nature of the CNTsdisplay unusual characteristics due to the coupling reactions ofreactive species electrochemically generated at either side of thegraphene lumen interphase.

CNT Growth Process: Aligned Multiwalled MWNTs by Thermal Chemical VaporDeposition.

MWNTs (CNT's) may exist as single-walled graphene cylinder structures(SWNT) or Concentric cylinder structured multi-wall MWNTs (MWNT)(Dresselhaus, M. S; Dresselhaus, G. and Eklund, P., Science ofFullerenes and Carbon) (Ebbsen, T., MWNTs, CRC Press, Boca Raton, Fla.,(1997)) (Saito, R.; Dresselhaus, G. and Dresselhaus, M. S., PhysicalProperties of Carbon). The MWNT growth processes adapted for thisinvention can be based on Chemical Vapor Deposition (CVD). The primaryrequirements for CNT growth are; a catalyst consisting of transitionmetals (i.e., Fe, Ni, Co), Carbon source and high Temperature (500-900deg.C.).

A. Gas Phase Thermal CVD Method:

The CVD reactor is sealed and flushed with Ar (100-300 Seem) gas for20-30 minutes. The whole furnace is set at 900° C. Ammonia is introducedin the system at a flow rate ranging from 20-250 Sccm, when the furnacetemperature exceeds 600° C. The substrate is treated with ammonia gasinside the furnace for 15-20 minutes to form nanometer size catalyticparticles. When the furnace temperature reaches the set value, Acetyleneis introduced in the gas feed with a flow range of 20-300 Seem. The flowratio of ammonia and acetylene is optimized to get uniform ACNTs array.Acetylene gas is the source of carbon for the growth of the nanotubes.The growth time ranges from 10 to 30 minutes depending on the CNT lengthrequired.

B. Solid Precursor Thermal Method:

Iron (ID phthalocyanine is used as both the carbon source and thecatalyst for preparing aligned MWNTs (Huang, S.; Dai, L. and Mau, A. W.H., J. Phys. Chem. B. 103, 4223 (1999)). The substrate (Silicon Chip) iscleaned with acetone in an ultrasonic bath, rinsed with acetone againand finally dried in air before placing it in zone 2 (1230) of the flowreactor (1214) (quartz tube) (1214) (refer FIG. 12). Iron (II)pathalocyanine (0.3-0.5 g) is placed in another quartz/ceramic boat andplaced in zone 1 of the quartz tube. The whole system is sealed andflushed with argon (Ar) for 20-30 minutes. This step removes any oxygenpresent in the quartz tube and provides an inert reaction atmosphere.The flow rate of Ar is reduced to 10 Seem and H₂ is introduced in thegas flow at 20 Seem. The gas flow is maintained steady through out thereaction. The temperature of zone 2 is set at 550° C. Zone 1 temperatureis set at 500° C. As zone 1 attains the set temperature, the pyrolysisof the organometallic precursor is triggered inside the furnace. Iron isreleased into the gas phase and gets spread inside the furnace and ontothe substrate via the Ar/H₂ gas flow. The pyrolysis step is maintainedfor 5 minutes. Following the pyrolysis step the zone 2 temperature isset to 900° C. and zone 1 is set to 800° C. As the temperature of zone 1ramps up the organometallic precursor remaining in the boat startsdecomposing, releasing carbon in the gas phase. The carrier gastransports the carbon in the gas phase to the high temperature zone 2where the growth of MWNTs on the quartz plate is initiated by the metalcatalyst. The furnace is maintained for 10 minutes when zone 1 and zone2 reach their set temperatures. After the reaction time, the furnace isshut-off, the H₂ flow is turned off, and only Ar gas flow is maintainedsteady at a low flow rate. The black layer that forms on the Sisubstrate is analyzed ant micron resolution by SEM and subsequently atsub-micron resolution by transmission electron microscopy (“TEM”).

C. Plasma Enhanced CVD (PECVD), Patterned Growth Method:

The MWNTs can be grown in a bell jar vacuum chamber at a base pressureof ˜10-2 Torr. Si/SiO2 and Si/TiN substrates with Ni metallizationpatterns can be used for PECVD patterned CNT growth. The metal catalystfilm thickness ranges from 50-150 nm. The substrate is place in thechamber and pumped down to ˜10-2 Torr pressure, at a temperature settingof 700° C. Ammonia etch gas (50-200 Sccm) is first introduced into thechamber for 5-10 minutes and subsequently followed by CNT growthacetylene gas at a nominal gas flow ratio (1:2-5) of acetylene toammonia. The glow discharge plasma generator is set at 0.5-1 kV de anddepositions can be carried out at a bias current of ˜0.1 A. The growthreaction time can vary from 5-20 min depending on the required length ofMWNTs and growth is observed only where the metal catalyst particleresides.

CNT Cladding Methods: Polymer CNT Claddings by Electrolytic Method:

Conductive polymer films can be deposited electrolytically by monomerreduction at an electrode surface. Monomer reduction generates freeradical that initiates and propagates the polymer synthesis (i.e.,polymerization). Polymerization terminates when current ceases and thesurface is passivated to electrolysis. Electrolytic polymerization isaccomplished with suitable monomers including aniline, pyrrole,thiophene, phenol, or any combination thereof.

(i) Polypyrrole Cladding Method by Constant Voltage Electrolysis:

A potential of 1.0 V (VS. Ag/AgCl) is applied for 90 s in an aqueoussolution of 0.1 M pyrrole and 0.1 M sodium per chlorate. Polypyrroledeposition is achieved on an aligned MWNT electrode. The electrolysiscurrent exponentially decays during the polymer film formation and is aclear indicator for complete polymer coverage of the CNTs. Claddingformation is verified by SEM pre and post-electrolysis

(ii) Polyaniline Cladding Method by Voltage Scan Electrolysis:

The cyclic voltametric technique is effective for the preparation ofaligned MWNT/polyaniline films. An aqueous electrolytic solution of 0.05M aniline with 0.1 M of sulfuric acid is used to electrochemicallydeposit polyaniline over individual aligned MWNT surface. Controllingthe scan rate and the number of cycles, a uniform and smooth coat ofpolymer can be obtained on the surface of the individual alignednanotubes. Cyclic scanning of voltage allows for more controlleddepletion of monomer during the electrolytic polymerization resulting inmore uniform films.

B. Cladding of ACNT Surface by Plasma Polymerization Technique:

RF Plasma polymerization of dielectric monomers such as aliphatichydrocarbons, substituted hydrocarbons, etc. is an attractive surfacepolymerizartion method of typically unreactive molecules to createdielectric films. A bell jar type reactor can utilized with radiofrequency glow discharge to initiate and propagate polymerization. Theadded advantage is that these films includes created at low pressure inthe gas phase under in clean-controlled environments (Iriyama, Y.;Yasuda, T.; Cho, D. I. and Yasuda, H., J. Appl. Polym. Sci. 39, 249(1990)) (Terlingen, J. G. A.; Gerritsen, H. F. C.; Hoffman, A. S. andFeijen, J. J. App Polym. Sci. 57, 969 (1995)) (Terlingen, J. G. A.;Gerritsen, H. F. C.; Hoffman, A. S. and Feijen, J. J. Appl Polym. Sci.57, 969 (1995)). The process is quite generic for deposition ofpolymers16 (For a general reference on plasma polymerization, see: (a)Yasuda, H. Plasma Polymerization; Academic Press: Orlando, (1995). (b)van Os, M. T.; Menges, B.; Fo{umlaut over ( )}rch, R.; Knoll, W.;Timmons, R. B. and Vancso, G. J., Mater. Res. Soc. Symp. Proc., 544,45(1999) (c) Hsieh, M. C.; Farris, R. J.; McCarthy, T. J.Macromolecules, 30, 8453 (1997) (d) Chatelier, R. C.; Drummond, C. J.;Chan, D. Y. C.; Vasic, Z. R.; Gengenbach, T. R.; Griesser, Langmuir, T.J., 11, 4122 (1995)), for immobilization of surfactant molecules17(Terlingen, J. G. A.; Feijen, J.; Hoffman, A. S. J., Colloid InterfaceSci. 155, 55 (1993)), or etching of the specimen surfacel8 (Manos, D. M.and Flamm, D. L., Plasma Etching, An Introduction, Academic Press:Boston, (1989)). The system depicted in FIG. 13 can be utilized forradio frequency sputtering and plasma polymerization.

FIG. 13 illustrates a radio frequency deposition system (1300) having asubstrate (1302), sheath (1304), target (1306), excitation electrode(1308), insulation of excitation electrode (1310), discharge glow(1312), passage to pumps (1314), inlet for monomer gas or argon gas (M,Ar)(1316), shutter (1318) and power supply (1320) indicated by radiofrequency.

Procedure to coat ACNT surface uniformly with hexane plasma layer isexplained. A plasma reactor powered by a commercial high voltageradio-frequency generator operating between 100-500 KHz (AG0201HV—ACD)can be used to carry out the surface modifications of aligned MWNTs. Theplasma chamber is connected with a plasma generator and a vacuum line. Afilm of aligned MWNTs is placed inside the plasma chamber on theelectrode. A small quantity of a liquid monomer (hexane) is introducedin the monomer bottle. High vacuum (˜0.1 Torr) is created in thechamber, before the admission of the monomer particles in the glasschamber. Once the desired monomer pressure (˜0.15-0.7 Torr) is attained,a radio frequency generator is turned on (Power—30 W, Freq—250 KHz) forthe desired discharge period (30-120 s) during which time the alignedMWNT surface is modified with plasma.

CNTs Doping Chemistry.

The doping of CNTs is accomplished in several ways; by direct chemicalbonding of functional groups on the RF plasma oxidized graphene carbon,by filling the CNT lumen to create peapods and, by forming a polymerfilm (cladding) on the graphene surface. Any of all combinations ofthese doping procedures can be useful in creating chemically selectivesensing devices.

CNT peapods can be filled with ionophores from the class of such ligandsas; cyclic poly-ethers (cryptands, calyxarenes), natural antibiotics(Valinomycin, Monensin, Nonactin) and other linear ion coordinationligands known in the art (Reference Ionophore literature). Such ligandsselectively bind the ion into the CNT phase and the charge accumulationis determined by complex formation constant equilibrium, solubilityfactors and ion (CNT/solution) partitioning factors. Because the CNT iscompletely neutral to all ions in a sample, only the primary ionexchange will result in a charge gradient formation within the CNT.Conventional ISE membranes respond predominantly to the ionophore-boundion, but can be susceptible to ion exchange with the polymer sites.Secondary ion interaction of the dielectric membrane contributes tobackground signal and thus, limits the detection sensitivity.Theoretically, this new ion selection mechanism can lower the detectionlimit from 10[−8] Molar (state-of-the-art) to ˜10[−12] Molar. Althoughthis level of selectivity and sensitivity is not required for wateranalysis, it may be important to medical/pharmaceutical applications.Such CNT constructs can be much more durable than conventional membranesensors that are susceptible to hydrolytic break down in water.Furthermore, the ionophores can be trapped within the CNT and will notleach as do conventional polymeric membranes.

Several electron mediators can effectively bridge the band gap andmediate electron transfer with solution or within the CNT/polymer phase:Ru(bpy)₃2+, Fe(bpy)₃2+, Ru(NH₃)₆3+, Tetracyanoquinodimethane (TCNQ),Quinone, Benzophenone, Ferrocene, TetramethylI-p-phenylenediamine(TMPD),Tetrathiafulvalene, Tri-N-p-tolylamine(TPTA). Such polymers, whetherelectron donors or acceptor or ion exchangers/ion carriers or redoxcenters, all can be coated onto the CNT by electrolytic polymerizationor RF plasma. These films can be easily applied as coatings on the outerCNT surface.

The CNT carbon structure is chemically altered by oxidative RF Plasma toactivate the carbon surface and create oxide, hydroxide, carboxyls andphthalic anhydride which will subsequently chemically bond withappropriate functional groups COOH, CONH2, COOCH3, OSiORx, etc. toprovide chemical reactive functionality for Schiff base, carbodiimide,amide, etc. linkage to peptides (antibody, enzymes, DNA).

CNT Doping Method by Supercritical CO₂ I. Super Critical CO₂ AssistedMWNT Doping (Peapod Formation).

Goal: To drive target molecule (e.g. Ru(bpy)₃ ²⁺, C₆₀) into the cavityof MWNTs.Materials: Silicon chip with CNT array pattern [FIG. (1)], Fullerene(C₆₀), Ru(bpy)₃ ²⁺.Solvents: 1,2-Dichlorobenzene, Chloroform, Tetrahydrofuran, Carbondisulfide, Ethanol, Toluene, De-ionized Water.Experimental Procedure: Aligned CNT Arrays Filled with Ru(Bpy).

-   -   (i) CNT-chip preparation: (Air oxidation-Optional): Heat the        SWNTs under oxygen in a muffle furnace at 600° C. for ˜5        minutes. Weigh the CNT chip after heating, the mass of nanotubes        should reduce to 30-50% of its original mass (˜6-10 mg).    -   (ii) Prepare a solution of Ru(bpy) in de-ionized water (e.g. 5        ml of 1 mM solution).    -   (iii) Place a drop of the solution mixture the chip and dry in        air.    -   (iv) Introduce this wafer into the supercritical chamber. Fill        the chamber with liquid CO₂.    -   (v) Attain super criticality and maintain a pressure of 100-150        bar @ 50-60° C. temperature for 3-4 hrs.    -   (vi) Collect the sample on the wafer; wash it with copious        amount of de-ionized water to remove any molecules absorbed on        the sidewalls of the nanotubes.    -   (vii) Characterize the sample by SEM/TEM.        II. Super Critical CO₂ Assisted Impregnation of Ionophores onto        CNT Surface.        Goal: To drive target molecule (e.g. 18-Crown-6,        Potassium-ionophore) into the cavity of MWNTs.

Materials: Cladded MWNTs, Fullerene (C₆₀), Ionophores, Trial Solvents:Chloroform, Tetrahydrofuran, Ethanol, Toluene, De-ionized Water.Experimental Procedure:

-   -   (i) Prepare a film of aligned CNTs on a chip. Perform conformal        cladding on the surface of the aligned CNTs.    -   (ii) Prepare a solution of 18-Crown-6 in Chloroform (e.g. 5 ml        of 1M) in a vial.    -   (iii) Introduce the cladded—aligned CNT sample into the vial        solution.    -   (iv) Place this vial in a super critical CO₂ chamber. Seal the        chamber.    -   (v) Fill the chamber with liquid CO₂.    -   (vi) Super critical conditions are achieved and thereafter the        pressure is maintained at 100-150 bar @ 50-60° C. for around 3-4        hrs.    -   (vii) The chamber is brought back to Room Temp and Pressure in a        controlled manner, so that the dried contents remain in the        sample vial.    -   (viii) Collect the cladded aligned CNT sample and characterize        it by SEM/TEM.

Example #1 Chlorine Detection

Free Chlorine [HClO] and Total Chlorine [HClO & RHNCl & Cl—RH] may bedetected with the Device in FIG. 1) when the CNTs are configured as aWorking Electrode in an electrolytic cell configuration. By theapplication of the appropriate voltage bias of 1.1V vs. Ag/AgCl (Ref.)free Chlorine (or HClO) will directly reduce in water according to thefollowing reactions:

A. Free Chlorine Measurement with No Dopant Requirement:

Cl2(g)+H2O═HClO+HCl [pK(a1)=3.5]

HClO═H⁺+ClO− [pK(a2)=7.5]

HClO+2e−+H2O═HCl+H2O2

The CNT islands in FIG. 3) are defined Working electrodes patterned fromthe Ni catalyst surface film. E-beam lithography can define the Ni filmpatterns with a resolution of 20-100 nm. Within this pad dimension,several CNTs will grow to form the working electrode. The ensemble ofthese 100 nm CNT islands make up the total working electrode surface. Asdepicted by the above electrochemical reaction, HClO will reduce to HCland other chlorinated hydrocarbons and amines will similarly reduce atvarious voltages (energies). Scanning bias voltages will induceelectrolysis of electro-active sample species such that independentresponses can be evoked at various voltages. The additional applicationof periodic perturbations (i.e., sinusoidal, pulse, etc.,) enhance thesensitivity and resolution of such electrolytic responses. Digitaldomain processing allows for deconvolution of response artifacts andnoise filtering. Such signal processing techniques improve sensitivityand specificity by isolating signal from background and by resolvingcomplementary signals in the time (kinetic) and voltage (energy) scale.

B. Total Cholorine by Iodide/Iodine dopant mediator:

½Cl₂+I−═Cl−+½I₂

RHNCl+I−═Cl−+RNH₂+Cl−+½I₂ Etc.

As the above reactions indicate, Iodine is a chemical reducing agent forchlorine and the I2/I− is also electroactive so that it not mediateselectron transfer through the CNT but can also be reversibly regeneratedafter chlorine oxidation. All chlorinated organic species such aschloramines (disinfection byproducts) and oxichlorides can be reduced byiodide, hence, iodine content is a measure of total chlorine.

To effect total chlorine reduction, the CNTs can be doped with Iodine:

Method 1: The CNT sensor pad of FIG. (1) comprising of aligned CNTs(arrays) is oxidized in a furnace at 400 deg C to create defects in theCNT. The CNTs are subsequently treated with supercritical fluidcomposition containing Iodine to effect phase transfer of iodine intoCNT.

Method 2: The vertically aligned CNTs (array) is coated with polyanalineconductive polymer by electrolytic deposition from aniline monomer andsubsequently impregnated with iodine by the scCO2.

Method 3: The vertically aligned CNTs (array) is coated with aliphatichydrocarbon dielectric polymer deposited by RF plasma free radicalpolymerization of n-hexane. The dielectric polymer is subsequentlyimpregnated with iodine by the scCO2 method above.

The total DC current measured corresponds to the rate of iodinereduction and reflecting the sum total of all chlorinated species thatoxidize iodide ion to iodine. Both CNT peapods and cladded CNTs behavesimilarly in this mechanism as mediators, however, the peapod is afaster reaction since the electrons can be exchanged directly(tunneling) with the graphene CNT structure. In the case of thepolyanaline cladded CNTs, the polymer phase conduction is likely tooccur via a donor acceptor “electron hopping” mechanism.

C. Luminescence Detection Mechanism for Tot Chlorine:

CNT peopods are generated by the scCO2 method using the redox mediatorRu(II)(bpy)2 as photo-emitter. The CNT peapods are cladded by dielectrichydrocarbon polymer (poly-n-hexane) by the by RF-plasma free radicalpolymerization method. The cladding is then pregnated with Ru(II)(bpy)2by the scCO2 method. Samples containing chlorinated organics will reactwith Ru(II)(bpy)2 to yield the oxidized state Ru(III) state within thecladding while peapod Ru(II)(bpy)2 is reduced electrolytically to Ru(1).This dynamic generation of Ru (I) and Ru(III) will luminesce at 610 nmand modulated by the sample chlorine. The emission is detected byphoto-diode.

Example #2 Calcium Ion Detection: Charge Coupled Devices

The passive device of FIG. 1) may be applied as an ion selective ionsensor by doping the CNT array with ionophore or ion exchange ligands.Such a sensor responds to the test sample ion content according to theequation:

E=E ^(o) +S ln[a _(i) +KijΣaij−E _(ref)]

where;

-   -   E^(o) is the standard potential (ln a_(i) intercept)    -   (S ln a_(i)−E_(ref)) is the chemical potential term for the ion        i.    -   Kij Σaij is the interference error term for ion j.

The assumptions are; E is referenced to Eref, slope is 50 mV for n=1,ionic strength is constant or activity coefficients χ=1, and Kij=>0.Hence, the CNT E response is a Log function of the target ionconcentration (or ai).

The doping of the CNT with ionophore may assume the “peapod” structurewith ionophore occupying the CNT interior void space. Alternatively,doping may be achieved by dielectric polymers coating (cladding) the CNTand impregnating the polymer with ionophore (See FIG. [10]). Examples ofcalcium specific ionophore and other ionophores significant to wateranalysis are given below:

ETH 1062—Calcium Ionophore

N,N,N′,N′-Tetrabutyl-3,6-dioxaoctanedi(thioamide)

ETH 129—Calcium Ionophore

N,N,N′,N′-Tetra[cyclohexyl]diglycolic acid diamideN,N,N′,N′-Tetracyclohexyl-3-oxapentanediamide

ETH 6010—Carbonate Ionophore

Heptyl 4-trifluoroacetylbenzoate

Proton ionophore I—pH

Tridodecylamine-Molecular Formula [CH₃(CH₂)₁₁]₃N

Potassium Ionophore Valinomycin-Molecular FormulaC₅₄H₉₀N₆O₁₈

Sodium Ionophore

Bis[(benzo-15-crown-5)-4′-ylmethyl]pimelate

Molecular Formula

C₃₇H₅₂O₁₄

2,3:11,12-Didecalino-16-crown-52,6,13,16,19-Pentaoxapentacyclo[18.4.4.4^(7,12).0^(1,20)0.0^(7.12)]dotriacontane

DD-16-C-5 Molecular Formula

C₂₇H₄₆O₅

The FIG. [2] schematic is that of a doped CNT assembly (200). Here, aMOSFET Charge Coupled device can be constructed by standard ICmanufacturing methods. The gate oxide (222) is coated with a(non-templated) array of aligned CNTs (238). The gate oxide (222) iselectrically insulated from the p-doped channel (202) so that theresulting high input impedance ensures that charge coupling willmodulate the gate electric field and consequently, the electronconduction between source (240) and drain (230). The CNT functions as anantenna to accumulate charge from solution contact to generate anelectric field (not shown) that in turn modulates the p-channel MOSFETdrain current according the simplified general formula: (J. Janata, et.al., in “Ion Selective Electrodes in Analytical Chemistry”, V 2, HFreiser Ed., Plenum Press, 1980)

I _(D) /kR _(Ω)=(V _(G) −V _(T) +S ln a _(i) −E _(ref))

where;

-   -   k is a constant re. CNT dimensions and e-mobility    -   ID is the drain current    -   R_(Ω) resistance of the CNT channel    -   V_(G)−V_(T) represent gate and threshold voltages    -   (S ln a_(i)−E_(ref)) is the chemical potential term for the ion        i.

This structure will respond only to chemical interactions on the CNTsurface when doped with ion specific ionophore (i.e., 18-crown-6 cyclicpolyether). The ionophore selectively binds ion (i.e., K+) specificallyfrom solution to charge the CNT, which in turn modulates the p-channelsemiconductor space charge. The chemical modulation may be measured as agate voltage at constant drain current or modulated drain current atfixed gate bias voltage.

All CNTs (antenna filed) can respond to the same chemical entity (i.e.,ion) for proper CNT-gated FET function. The signal-to-noisecharacteristics of such a CNT-gate FET is significantly superior to thecomparative passive sensor (CNT-array), but all thermodynamic andkinetic response characteristics remain the same. The nanoantenna CNTchemical sensor is sensitive and specific (relative to themacro-membrane equivalent) because the signal focuses on the ionexchange interaction only and all artifacts regarding CNT chemicalinteractions liquid junction ion fluxes, etc., are non-existant.

Charged coupled mechanism of detection is based on the selectivegeneration of an electric field on a CNT as a consequence of ion(charge) capture as described by the equations above, the solutionchemical potential affects the gate voltage that modulates the source todrain current of a nominally operating FET device.

This MOSFET sensing device shown is a p-n-p FET operating in theinversion mode (large reverse voltage bias). The CNTs function asantennas and as a metal coating on the metal oxide insulator (MOI gate).The FET may or may not be operated in the Field Effect mode but as aconventional transistor with forward or reverse gate bias. In thereverse bias mode the CNT may operate as an ion-gated switch, in theforward gate bias mode as ion modulated drain current.

Several highly selective cationic ionophores for Calcium, Potassium, andSodium ions and H+ and CO3=anion exchangers are shown above. Suchionophores target the Potable Water Panel of Table I. The ion exchangepolymers shown of FIG. [8] and the donor/acceptor polymers of FIG. [9]offer fixed site polymer structural cladding alternatives for stableselective chemistry. Ion exchangers such as polysulfonates (cationic)and quaternized polyalkylammonium (anionic) are effective fixed sitecharge conductivity mediators for cladded CNTs. The p/n modifiers(electron donor/acceptor polymers) are effective mobile electron/holemediators for chemically modulating CNT transconductance.

Redox reactions can also apply to modulate Gate bias. Iodine cladded CNT(I2/I-couple) will oxidize chlorine to form Iodide ion. Hencedonor/acceptor polymers based on Iodine as an electron acceptor dopantwill mediate both conductivity and charge and is adaptable to either FETstructure discussed above. Reduction-oxidation reactions in general;TCNQ/TCNQ= and Ru++/Ru+, etc. will modulate gate bias by charge ratioand/or conductivity and hence may be coupled to target molecules ofinterest for application on FET devices.

Example #3 Ammonia & Carbon Dioxide Detection

The sensor of FIG. 10) is based on the cladded peapod structure of FIG.(7). It couples the ammonium ion specific CNT peapod with a gas barrierpolymer cladding. PTFE cladding is an effective NH3 gas separator fromdissolved NH++OH− (ammonia) in solution. Nonactin is a selectiveionophore for NH4+ that is immobilized within the peapod. NH3 permeatesthrough the cladding and NH4+ is captured and bound by the nonactin togenerate CNT charge.

Similarly, CO2 can permeate gas barrier (cladding) to bind with Heptyl4-trifluoroacetylbenzoate as carbonate anion. Alternatively, CO2 can bedetected as a pH change with Tridodecylamine. Both mechanisms separatethe gas from solution and generate ionic charge on the CNT. Themeasurement is accomplished by electromeric EMF measurement of a passiveCNT array sensor or by active CNT-gated FET device. In either case thechemical potential of the NH4+ or CO3″. is in equilibrium with the EMFof the CNT.

Example #4 Sarin Toxin Detection

(By Acetylcholinesterase (choline hydrolysis) inhibition reaction):Sarin (O-isopropyl methylphophonofluoridate) inhibits thechlorinesterase catalyzed hydrolysis of acetylcholine to choline(quaternized ammonium salt). The quaternary ammonium ion is detected bycationic exchanger shown in FIG. 8) as modulated CNT conductivity. TheCNT can be either peapod or ionic polymer cladded CNT. Cyclicpoly-ethers can be selective to quaternary ammonium cations, albeit lessselective than smaller ion sizes.

Example #5 Sarin Toxin Detection

(By ImmunoAssay): Anti-Satin capture antibody is Sandwiched withAnti-Sarin Urease conjugate. Step I is top capture Sarin on Nonactin CNTpeapods with Anti-Sarin antibody. Step II is to sandwichAnti-Sarin-Sarin- and Urease Anti-Sarin Conjugate. Detect ammonium iongenerated by Urease conjugate label captured at CNT peapod surface.

In this detection scheme the combined specificity of enzyme catalysis tothe specific detection of the ion generated (ammonium in this case)yields exceptional sensitivity and detection specificity. And thissensor design approach is entirely generic with respect to sandwichimmunoassay mechanism. The detection scheme is the same, i.e., match theenzyme label (antibody conjugate) to the product of the enzyme reactionfor chemical amplification and the capture antiboby for specificity. Thegeneration of label ion is confined to the cladding surface of the CNT(or peapod) concentrating ion product at the detection surface and thesensitivity multiplies many fold. This scheme is repeated with redoxactive label antibody conjugates as is the case for horse radishperoxidase (HRP) that generates peroxide on the FET gate surface.Peroxide reacts with I2/1− or Ru2+/Ru+ dopants to alter charge and/orconductivity

Example #6 Microbial Identification (E. coli)

Oligonucleotide sequences that are complementary to target E. coli DNAsequences will hybridizate to form dsDNA. When such hybridizations areconfined to the CNT surface, the hybridization event may be detected byintercalation of transition metal ions. In the case of dsDNAhybridization on the CNT-gated FET intercalated ions, e.g., Ag+, Ru++,etc. would be detected by CNT gate voltage bias that is modulated byintercalated ion or by redox electrochemistry of the intercalated metalions

To overcome the problem of mutant mismatch (false negatives or falsepositives) the Randomly Amplified Polymorphic DNA approach would be usedwith a high debsity CNT sensor array to detect polymorphism populationsof DNA amplicons with subsequent pattern analysis.

TABLE I A potable water panel comprising ac chemistry profile that is ameasure of water quality Water Parameters Test Selective ChemistryRange-(Molar Units) Potassium K⁺ Valinomycin- ISFET 10⁻⁵-10⁻¹ Sodium NA⁺Calyxarene- ISFET 10⁻⁴-10⁻¹ Hydronium pH Tri-n-dodecylamine- ISFET 5-9Calcium Ca⁺⁺ ETH 1001- ISFET 10⁻⁵-10⁻² Chloride Cl⁻ Quatemary AmmoniumPolymer - ISFET 10⁻⁴-10⁻¹ Alkalinity HCO3⁻ PTFE cladding/pH-FET 3 ×10⁻³-10⁻¹ Oxygen pO₂ PTFE cladding/Peapod Electrode 0-300 mmHg AmmoniapNH₃ PTFE cladding/NH4+-FET 10⁻⁵-10⁻¹ Chlorine Cl₂ HOCl reduction-Peapod Electrode 1-10 ppm Oxidation - Reduction ORP CNT Potential 0-1000mV Temperature RTD, Diode 5-50° C. Conductivity Ti/Pt 0-2000 μS/cm

TABLE II DRINKING WATER MONITORING APPLICATION CNT-array DopantsChemistry Sensor Category Target Analytes Dopants/Chemistry IonDetection (H+) Ca++, pH Peapod or cladding/(Ca) Ionophore/tri-alkylamineGas Detection Ammonia; Cladded (dielectric)/Peapods (Nonactin-NH4+)Carbon Dioxide Cladded (dielectric)/tri-alkylamine (H+) Oxygen CladdedPeapod Redox Detection Free Chlorine; CNT - electrode Tot Chlorine RedoxMediator (I2), Peapod or cladding (polyanyline) ECL of Ru(bpy)₃ ²⁺Chloramines/ClO2 CNT-electrode Peapod or cladding doped w. Iodine orTCNQ Toxins by Enzyme Toxins Acetyl Choline Esterase InhibitionInhibition Sarin/Risin etc. Immuno-assay by Cladded-Peapod ByImmuno-sensor Donor-Acceptor (Clading or Peapod) Ion Detection (Cladingor Peapod) Redox Mediation (Clading or Peapod) ECL/Peapod-Cladding ComboChloro-Alkylamines Cladded Peapods Ions/donor-acceptor/redox/ECLMicrobes by DNA Cladded Peapods HybridizationIons/donor-acceptor/redox/ECL

TABLE III CNT SENSORS Fab Process NT Structure Chemistry AnalyticalMethod Target Analytes CNT arrays-undoped CNT arrays CVD growth Votageprograms; a.c. HCIO, O2 voltammetry R—NH—Cl, Clo2 CNT Islands CVD growthVotage pulse transients HCO—Cl, Cl—CH2—CO CNT-gate CNT gate-MOSFETFourier Analysis of transients ECL I-V measurements Cladded CNT'sDielectric Cladding Ionophores Potentiometry NH3, CO2 (gasses) IonophoreRedox Capacitance Ca++, pH Functionalized Donor-Acceptor NT ConductivityHClO, O2 Conductive polymer Selective I-V R—NH—Cl, CIO2 cladding HCO—Cl,Cl—CH2—CO Redox Functionalized Peapod CNTs Polymer grafts PotentiometryEnzyme assays Dielectric Cladding Ionophores Capacitance BiotoxinsIonophore Functionalized Conductive polymer Redox NT ConductivityImmuno-assays cladding Donor-Acceptor Selective I-V Biotoxins RedoxFunctionalized Electro- Microbes Fluors chemiluminescence FluorescenceNH3, CO2 Nanotitrations Ca++, pH Functionalization (NT's, peapods,Ionophores Potentiometry Enzyme assays claddings, Redox CapacitanceBiotoxins combinations) Donor-Acceptor NY Conductivity Immuno-assays ofpeapods Proteins Selective I-V Biotoxins of claddings Enzymes Electro-Microbes of NTs chemiluminescence Antibodies Fluorescence NH3, CO2 DNACa++, pH Carcinogens

TABLE IV Reference numerals description used in the figures. FIGS. 1A +1B: 100 doped CNT assembly electrode 102 substrate (oxidized siliconwafer) 104 electrically conductive layer (TiW/Mo/TiW/TiN) 106 catalyst(Ni) 108 metal layer (Cr/Au) 110 passivation layer (Silicon Nitride) 118assembly of doped MWNTs FIGS. 2A + 2B: 200 doped CNT assembly FET 202p-doped 214 thermal-oxide (insulating layer) 218 silicon nitride(protective layer) 222 gate oxide 224 catalyst layer 230 drain 238 arrayof aligned CNTs 240 source 234 silicon nitride FIGS 3A + 3B: 300 a dopedCNT assembly electrode array 302 substrate 304 thermal oxide layer orelectrical conductive layer 306 nickel catalyst layer 308 metal contactlayer 310 electrically conductive layer or silicon nitride insulatinglayer 316 contact holes 318 MWNT bundles 328 nickel metal interface FIG.4: 400 integrated multisensor 402 CNT assembly FET 404 CNT assemblyworking electrodes 422 CNT assembly working electrodes 424 CNT assemblyworking electrodes 406 electrical contacts 408, 416 electrical leads tocounter electrode 410, 434 reference electrodes for electrolytic cell412 counter electrode 414 substrate 418, 432 electrical leads toreference electrodes 410, 434 420 ? gate lead to CNT assembly FET 402426 ? source lead to CNT assembly FET 402 428, 430, electrical leads toCNT assembly 436 working electrodes to 422, 424, 404 FIG. 5: 500vertically aligned doped CNT containing a fill material and having acladding 502 CNT 504 fill material 506 catalyst layer/electricallyconductive layer/substrate 508 cladding FIG. 9: 900 doped CNT arrayworking electrode 902 substrate 904 thermal oxide layer 906 electricallyconductive layer 908 metal contact pad 910 silicon nitride passivationlayer 912 electrical contact hole 914 reactive ion etching 916vertically-aligned MWNT array 918 chemically functionalized CNTs FIG. 10(a-r): 1000 CNT-gated MOSFET 1002 substrate 1004 pad dioxide layer 1006silicon nitride layer 1008 silicon recess etch 1010 boron 1012 fieldarea 1014 thermal oxide (silicon dioxide) 1016 sacrificial gate oxide1018 poly silicon 1020 source and drain areas 1022 2nd gate oxide 1024catalyst layer 1026 source + drain 1028 passivation layer (siliconnitride) 1030 contact holes 1032 CNT growth area 1034 metal contact 1036water exposed to acetylene + ammonia gas 1038 vertically-oriented CNTarray 1040 phosphorus ion implant 1042 dopant FIG. 11: 1100 Doped CNTassembly electrode array 1102 substrate 1104 thermal oxide layer 1106electrically conductive layer 1108 metal contact pad 1110 siliconnitride passivation layer 1112 electrical contact hole 1114 reactive ionetching 1116 vertically aligned MWNT array 1118 chemicallyfunctionalized CNTs FIG. 12: 1200 CNT flow reactor system 1202 gasreactants and carrier gas cylinders 1204 gas regulators 1206 gas feedinlet conduit 1208 mass flow meters 1210 channel readout 1212 flowreactor inlet gas conduit 1214 gas flow reactor exterior 1216 gas flowreactor exterior 1218 CNT solid catalyst (Iron Phtholo) 1220 quartzplate substrates 1222 furnace, zone 3 1224 temperature controllers 1226reaction exhaust vent 1228 furnace, zone 1 1230 furnace, zone 2 FIG. 13:1300 Radio frequency disposition system 1302 substrate 1304 sheath 1306target 1308 excitation electrode 1310 insulation of excitation electrode1312 discharge glow 1314 passage to pumps 1316 inlet for monomer gas orargon gas 1318 shutter 1320 power supply 1322 grounding wire 1324entrance for substrate 1326 substrate holder 1328 outlet for monomer gasor argon gas 1330 chamber housing 1332 Gauge Pump 1334 shutter feed-thru1336 insulators

A wide variety of doped antennae assembly electrodes, methods, sensors,and field-effect transistors, as well as associated methods ofpreparation are envisioned. For example, the doped antennae assemblyelectrode, can comprise: an electrically conductive layer at leastpartially surmounting a substrate; and an assembly of doped MWNTsvertically oriented with respect to the electrically conductive layer toprovide the doped antennae assembly electrode. The doped antennaeassembly electrode may further comprising a catalyst at least partiallysurmounting the electrically conductive layer, wherein at least aportion of the doped MWNTs are attached at their ends to the catalyst.The doped antennae assembly electrodes may comprise a plurality of MWNTshaving one or more fill molecules. The doped antennae assemblyelectrodes may have fill molecules that include molecules, molecularions, atoms, atomic ions, or any combination thereof. The doped antennaeassembly electrodes may have fill molecules that comprise one or morefullerenes, doped fullerenes, ionophores, ion exchangers, redoxmolecules, conductive polymers, or any combination thereof. The dopedantennae assembly electrodes may include ionophores that include cyclicpolyethers, antibiotics, linear chain ligands or any combinationthereof. The doped antennae assembly electrodes may have cyclicpolyethers that comprise 12-crown-4 to 24-crown-8 polyethers, or anycombination thereof. The doped antennae assembly electrodes may haveionophores that include one or more cryptands, calixarenes, rotaxanes,or any combination thereof. The doped antennae assembly electrodes mayhave fullerenes that include one or more of C60, C70, C80, C90, or anycombination thereof. The doped antennae assembly electrodes may includefullerenes that are doped fullerenes. The doped antennae assemblyelectrodes may include doped fullerenes that are filled, coated,chemically functionalized, or any combination thereof. The dopedantennae assembly electrodes may include ion exchangers that includequaternized PVC, sulfonated PTFE, or any combination thereof. The dopedantennae assembly electrodes may include antibiotics such asvalinomycin, nonactin, monensin, iosin, or any combination thereof. Thedoped antennae assembly electrodes may include linear chain ligands suchas poly-oxyethylene, tri-n-alkylammonium halide, or any combinationthereof. The doped antennae assembly electrodes may include fillmolecules that are semiconductor polymers comprising donor-acceptorpairs. The doped antennae assembly electrodes may include semiconductorpolymers that comprise donor-acceptor pairs include semicarbazole/TCNQ,ionene/iodine, or any combination thereof. The doped antennae assemblyelectrodes may include fill molecules that comprise conductive polymers.The doped antennae assembly electrodes may include conductive polymersthat comprise a polypyrrole, a polyaniline, a poly-p-phenylene, apolyacetylene, or any combination thereof. The doped MWNT assemblyelectrods may include at least two of the doped MWNTs that comprisedifferent fill molecules. The doped antennae assembly electrodes mayinclude fill molecules that include a chemical agent capable ofresponding to a chemical or an electrical signal.

The doped antennae assembly electrodes may include a plurality of MWNTshaving a cladding. The doped antennae assembly electrodes may includecladding that includes a dielectric, an ion conducting polymer, anelectron conducting polymer, an ionophore polymer dopant, aredox-mediator dopant, or any combination thereof. The doped antennaeassembly electrodes may include dielectric that includes a polyolefinpolymer, a polyaliphatic polymer, a polysiloxane polymer, a polyurethanepolymer, a polyvinylchloride polymer, alumina, or any combinationthereof. The doped antennae assembly electrodes may include ionconducting polymer that includes nation, polystyrene sulfonate,polyvinylpridinium, or any combination thereof. The doped antennaeassembly electrodes may include electron conducting polymer thatincludes a doped polymer, an electrochemically doped polymer, a redoxelectroactive polymer, or any combination thereof. The doped antennaeassembly electrodes may include doped polymer that includes apolyionine, a polysilicon, a polysemicarbazole, a polyphenylene, apolyacetylene, a polyphenylene sulfide, or any combination thereof. Thedoped antennae assembly electrodes may include doped polymer thatincludes a dopant, the dopant comprising AsF5, I2, Li, K, BF6-, PF6-, orany combination thereof. The doped antennae assembly electrodes mayinclude electrochemically doped polymer that includes a polypyrrole, apolythiophene, a polyphenylquinone, a polyaniline, or any combinationthereof. The doped antennae assembly electrodes may include redoxelectroactive polymers that include polyvidlogen, polyvinylferrocene,poly-Ru(vbpy)3++, or any combination thereof. The doped antennaeassembly electrodes may include ionophore polymer dopant that includes acrown ether, a cryptand, a sphereand, a rotaxane, an antibiotic, anon-cyclic ligand, or any combination thereof. The doped antennaeassembly electrodes may include redox-mediator dopant that includesRu(bpy)3++, Br2/Br−, Fe(phen)3+++, Co(terpy)2+++, Fe(CN)6(3−),Ru(NH3)6+++, quinone, hydroquinone, methylviologen,tetracyanoquinodimethane, benzophenone, ferrocene,tetramethyl-p-phenylenediamine, tetrathiafulvalene, tri-N-p-tolylamine,or any combination thereof.

The doped antennae assembly electrodes may include cladding thatcomprises one or more functional reactive groups residing upon a surfaceof the cladding. The doped antennae assembly electrodes may includefunctional reactive groups that include an oxide, a hydroxide, acarboxylic acid, an ester, an ether, a carbonyl, an amine, an amide, anepoxide, a halide, or any combination thereof. The doped antennaeassembly electrodes may include cladding that includes a linkerattaching the cladding to the doped MWNTs. The doped antennae assemblyelectrodes may include a linker that includes a Schiff base, acarbodi-imide, an amide, or any combination thereof. The doped antennaeassembly electrodes may include cladding linked to a selectivefunctionality on the surface of one or more of the MWNTs. The dopedantennae assembly electrodes may include selective functionality on thesurface of one or more of the MWNTs that includes a protein, aphospholipids, a nucleic acid, an electron mediator, an ionophore, orany combination thereof. The doped antennae assembly electrodes mayinclude protein that includes an enzyme, an antibody, or any combinationthereof. The doped antennae assembly electrodes may include nucleic acidthat includes an oligonucleotide, DNA, RNA, or any combination thereof

The doped antennae assembly electrodes may include at least two of thedoped MWNTs comprise different claddings. The cladded doped antennaeassembly electrodes may include cladding that includes a chemical agentcapable of responding to a chemical or an electrical signal. The claddeddoped antennae assembly electrode may include a chemical agent capableof responding to a chemical or an electrical signal.

The doped antennae assembly electrodes may include MWNTs that compriseone or more functional reactive groups covalently attached to thegraphene surface of the MWNTs. The doped antennae assembly electrode ofclaim 42, wherein the functional reactive groups include an oxide, ahydroxide, a carboxylic acid, an ester, an ether, a carbonyl, an amine,an amide, an epoxide, a halide, or any combination thereof. The dopedantennae assembly electrodes may include functional reactive groupscovalently attached to the graphene surface includes a linker attachedto the doped MWNTs. The doped antennae assembly electrodes may include alinker that includes a Schiff base, a carbodi-imide, an amide, or anycombination thereof. The doped antennae assembly electrodes may includefunctional reactive groups covalently attached to the graphene surfaceincludes a selective functionality. The doped antennae assemblyelectrodes may include selective functionality that includes a protein,a phospholipids, a nucleic acid, an electron mediator, an ionophore, orany combination thereof. The doped antennae assembly electrodes mayinclude protein that includes an enzyme, an antibody, or any combinationthereof. The doped antennae assembly electrodes may include nucleic acidthat includes an oligonucleotide, DNA, RNA, or any combination thereof.

The doped antennae assembly electrodes may include an electricallyconductive layer that comprises a metal, an electrically conductivepolymer, a carbon film, or any combination thereof. The doped MWNTassembly e electrodes may include an electrically conductive layer thatis a lead conductor residing between the substrate and the catalyst. Thedoped antennae assembly electrodes may include an electricallyconductive layer that comprises Pt, Au, Ti, W, V, Mo, or any combinationthereof. The doped antennae assembly electrodes may include metal thatcomprises a CVD-deposited metal. The doped antennae assembly electrodesmay include CVD-deposited metal that comprises TiW, Mo, TiN, or anycombination thereof. The doped antennae assembly electrodes may includean electrically conductive layer that is characterized as having a layerthickness in the range of from about 1 nanometer to about 1000nanometers. The doped antennae assembly electrodes may include anelectrically conductive layer that is characterized as having a layerthickness in the range of from about 10 nanometers to about 100nanometers. The doped antennae assembly electrodes may include anelectrically conductive layer that is characterized as having a layerthickness in the range of from about 50 nanometers to about 100nanometers.

The doped antennae assembly electrodes may include catalyst thatcomprises Ni, Co, Fe, Ru, Rh, Pd, Os, Ir, or any combination thereof.The doped antennae assembly electrodes may include catalyst thatcomprises an organo-metallic catalyst, an iron-phthalocyanine, acobalt-phthalocyanine, or any combination thereof. The doped antennaeassembly electrodes may include catalyst capable of growing MWNTs. Thedoped antennae assembly electrodes may include catalysts capable ofgrowing MWNTs such as nickel, cobalt, iron, or any combination thereof.The doped antennae assembly electrodes may include catalystcharacterized as having a layer thickness in the range of from about 1nanometer to about 10,000 nanometers. The doped antennae assemblyelectrodes may include catalyst characterized as having a layerthickness in the range of from about 500 nanometers to about 1000nanometers. The doped antennae assembly electrodes may include catalystcharacterized as having a layer thickness in the range of from about 700nanometers to about 900 nanometers.

The doped antennae assembly electrodes may include a plurality of dopedMWNTs perpendicularly oriented to the substrate. The doped antennaeassembly electrode of claim 65, wherein the doped MWNTs are orientedparallel to each other. The doped antennae assembly electrodes mayinclude a doped MWNT carpet, a doped MWNT array, or any combinationthereof. The doped antennae assembly electrodes may include anelectrically conductive layer that comprises a single contiguousconductive layer, and the doped MWNT carpet is in electricalcommunication with the single contiguous conductive layer. The dopedantennae assembly electrodes may include an aligned array of nanotubesof a defined geometry and pitch oriented with respect to theelectrically conductive layer. The doped antennae assembly electrodesmay include an array of doped MWNTs. The doped antennae assemblyelectrodes may include catalyst patterned on the electrically conductivelayer, and the assembly of doped MWNTs is attached to the patternedcatalyst. The doped antennae assembly electrodes may include catalystpatterned as an array of islands, stripes, circles, squares, rings,triangles, polygons, or any combination thereof

The doped antennae assembly electrodes can also be used as a workingelectrode in an electrolytic cell or sensor. The doped antennae assemblyelectrodes may include a substrate comprising quartz, aluminum oxide,alumina, silicon, a ceramic boat, chromium, iridum, aluminum, niobium,tantalum, titanium, tungsten, carbon, silicon oxide, silicon carbide,brass, bronze, silver, gold, glass, indium tin oxide, graphite,platinum, magnesium aluminum oxide, platinum crucible, magnesiumaluminate spinel, or any oxide, alloy, or combination thereof. The dopedantennae assembly electrodes may include one or more layers of quartz,aluminum oxide, alumina, silicon, a ceramic boat, chromium, iridum,aluminum, niobium, tantalum, titanium, tungsten, carbon, silicon oxide,silicon carbide, brass, bronze, silver, gold, glass, indium tin oxide,graphite, platinum, magnesium aluminum oxide, platinum crucible,magnesium aluminate spinel, or any oxide, alloy, or combination thereof.

Sensors may include any of the doped MWNT electrodes described herein.Likewise, field effect transistors may include any of the doped MWNTelectrodes described herein.

Methods of making doped antennae assembly electrodes may include thesteps of: surmounting a substrate with an, electrically conductivelayer; surmounting an assembly of MWNTs on the electrically conductivelayer, the MWNTs being vertically oriented; and doping at least aportion of the MWNTs with a cladding, a covalent bond linkage, afunctional dopant molecule, a fill material, or any combination thereof.The methods may include the step of surmounting the substrate with athermal oxide layer, and the electrically conductive layer surmounts thethermal oxide layer. The methods may include the step of surmounting thethermal oxide layer with an electrically conductive contact pad. Themethods may include the electrically conductive layer being surmountedto the substrate using a chemical vapor deposition process, a sputteringprocess, a fluid deposition process, or any combination thereof. Themethods may include a catalyst being surmounted to the electricallyconductive layer using a chemical vapor deposition process, a sputteringprocess, a fluid deposition process, or any combination thereof. Themethods may include the chemical vapor deposition process including agas phase thermal chemical vapor deposition method, a solid precursorchemical vapor deposition method, a plasma-enhanced chemical vapordeposition method, or any combination thereof. The methods may include achemical vapor deposition method including microwave stimulation, radiofrequency plasma stimulation, direct current plasma field enhancement,or any combination thereof. The methods may include the step ofsurmounting an assembly of MWNTs includes end-linking a plurality ofMWNTs to the conductive layer. The methods may include the plurality ofMWNTs self-assembling on the conductive layer.

The methods may include the MWNTs comprising an end-functionalized MWNT.The methods may include the conductive layer comprising functionalgroups that link to the ends of the MWNTs. The methods may include theMWNTs comprising an end-functionalized MWNT. The methods may include theMWNTs being provided as a dispersion of a plurality of MWNTs in a fluid,and the fluid may be an organic liquid, an aqueous liquid, or anycombination thereof.

The methods may include the step of surmounting an assembly of MWNTsincluding growing an assembly of MWNTs on the conductive layer. Themethods may include the step of growing an assembly of MWNTs includesgas phase thermal vapor deposition, solid precursor chemical vapordeposition, plasma enhanced chemical vapor deposition, or anycombination thereof.

The methods may include the step of surmounting an assembly of MWNTsthat includes surmounting the conductive layer with catalyst andcontacting a MWNT forming composition and the catalyst at conditionsnecessary to grow the assembly of MWNTs from the catalyst. The methodsmay include the step of growing an assembly of MWNTs that includes gasphase thermal vapor deposition, solid precursor chemical vapordeposition, plasma enhanced chemical vapor deposition, or anycombination thereof. The methods may include the MWNT formingcomposition comprising an organometallic precursor, or any combinationthereof. The methods may include the organometallic precursor comprisinga phthalocyanine, a porphorin, a carbon bearing ligand, or anycombination thereof. The methods may preferably include theorganometallic precursor comprising iron(II)phthalocyanine. The methodsmay include the carbon bearing ligand comprising a transition metalchelate including Fe, Co, Ni, Ru, Os, Eu, or any combination thereof.The methods may include the MWNT forming composition comprising one ormore molecules composed of covalently bonded carbon atoms, hydrogenatoms, oxygen atoms, nitrogen atoms, or any combination thereof. Here,the molecules include gases comprising methane, ethane, propane, butane,ammonia, acetylene, ethylene, propylene, or any combination thereof.Alternatively, the molecules may include liquids comprising aliphatichydrocarbons, olefins, or any isomer or combination thereof. Theconditions necessary to form the assembly of MWNTs may include atemperature in the range of from about 300° C. to about 1000° C. and apressure in the range of from about 10⁻¹ torr to 10⁻⁹ torr. Theconditions necessary to form the assembly of MWNTs may include atemperature in the range of from about 500° C. to about 700° C. and apressure in the range of from about 10⁻⁶ torr to 10⁻⁹ torr.Alternatively, plasma-enhanced chemical vapor deposition can be used toform the MWNTs.

The methods may include the step of doping that includes liquid coating,chemical vapor deposition, ion beam deposition, electrospray coating,supercritical fluid solute phase transfer, or any combination thereof.The methods may include ion beam deposition that includes electro-sprayionization, electron beam deposition, proton beam deposition, atomic ionbeam deposition, molecular beam deposition, or any combination thereof.The methods may further include the step of depositing a metal on theelectrically conductive layer to provide an electrode contact pad. Themethods may include the electrode contact pad being distally locatedfrom the assembly of MWNTs. The methods may further include the step ofpatterning the assembly of MWNTs. The methods may include the step ofpatterning to give rise to an array of MWNTs. The methods may includethe step of patterning that includes photolithography, UV lithography,e-beam lithography, reactive ion etching, chemical etching,nano-imprinting, electro-forming, or any combination thereof. Themethods may further include the step of patterning the electricallyconductive layer. Here, the step of patterning typically gives rise toan array of MWNTs. The step of patterning can include photolithography,UV lithography, e-beam lithography, reactive ion etching, chemicaletching, nano-imprinting, electro-forming, or any combination thereof.

The methods may include the step of surmounting the substrate with anelectrically conductive layer includes electroforming, electro-lessdeposition, electrochemical deposition, vapor deposition, sputtering, orany combination thereof. The methods may include using an assembly ofdoped MWNTs that comprise a plurality of MWNTs having a fill material.Fill material may include molecules, molecular ions, atoms, atomic ions,or any combination thereof. Fill material may include one or morefullerenes, doped fullerenes, ionophores, ion exchangers, redoxmolecules, conductive polymers, or any combination thereof. Ionophoresmay include ionophores include cyclic polyethers, antibiotics, linearchain ligands or any combination thereof. Cyclic polyethers may include12-crown-4 to 24-crown-8 polyethers, or any combination thereof.Ionophores may include one or more cryptands, calixarenes, rotaxanes, orany combination thereof.

The methods may include the fullerenes including one or more of C60,C70, C80, C90, or any combination thereof. The fullerenes can be dopedfullerenes. The doped fullerenes can be filled, coated, chemicallyfunctionalized, or any combination thereof. The methods may include ionexchangers including quaternized PVC, sulfonated TPFE, or anycombination thereof. The methods may include antibiotics that includevalinomycin, nonactin, monensin, iosin, or any combination thereof. Themethods may include linear chain ligands that include poly-oxyethylene,tri-n-alkylammonium halide, or any combination thereof. The methods mayinclude fill material that includes semiconductor polymers comprisingdonor-acceptor pairs Semiconductor polymers can comprise donor-acceptorpairs include semicarbazole/TCNQ, ionene/iodine, or any combinationthereof. Alternatively, the fill material can include conductivepolymers. Suitable conductive polymers comprise a polypyrrole, apolyaniline, a poly-p-phenylene, a polyacetylene, or any combinationthereof.

The methods may include at least two of the doped MWNTs comprisingdifferent fill molecules. For example, the fill material may include achemical agent capable of responding to a chemical or an electricalsignal.

The methods may include at least a portion of the MWNTs are doped with acladding. The cladding can include a dielectric, an ion conductingpolymer, an electron conducting polymer, an ionophore polymer dopant, aredox-mediator dopant, or any combination thereof. The dielectric caninclude a polyolefin polymer, a polyaliphatic polymer, a polysiloxanepolymer, a polyurethane polymer, a polyvinylchloride polymer, alumina,or any combination thereof. Ion conducting polymer can include nafion,polystyrene sulfonate, polyvinylpridinium, or any combination thereof.Electron conducting polymer can include a doped polymer, anelectrochemically doped polymer, a redox electroactive polymer, or anycombination thereof. The doped polymer can include a polyionine, apolysilicon, a polysemicarbazole, a polyphenylene, a polyacetylene, apolyphenylene sulfide, or any combination thereof. The doped polymer caninclude a dopant, the dopant comprising AsF5, I2, Li, K, BF6−, PF6−, orany combination thereof. The electrochemically doped polymer can includea polypyrrole, a polythiophene, a polyphenylquinone, a polyaniline, orany combination thereof. The redox electroactive polymers can includepolyviologen, polyvinylferrocene, poly-Ru(vbpy)3++, or any combinationthereof. The ionophore polymer dopant can include a crown ether, acryptand, a sphereand, a rotaxane, an antibiotic, a non-cyclic ligand,or any combination thereof. The redox-mediator dopant can includeRu(bpy)3++, Br2/Br−, Fe(phen)3+++, Co(terpy)2+++, Fe(CN)6(3−),Ru(NH3)6+++, quinone, hydroquinone, methylviologen,tetracyanoquinodimethane, benzophenone, ferrocene,tetramethyl-p-phenylenediamine, tetrathiafulvalene, tri-N-p-tolylamine,or any combination thereof.

The methods may include cladding that comprises one or more functionalreactive groups residing upon a surface of the cladding. The functionalreactive groups can include an oxide, a hydroxide, a carboxylic acid, anester, an ether, a carbonyl, an amine, an amide, an epoxide, a halide,or any combination thereof. The cladding can include a covalent bondlinkage attaching the cladding to the doped MWNTs. The covalent bondlinkage can include a Schiff base, a carbodi-imide, an amide, or anycombination thereof. The cladding can be linked to a selectivefunctionality on the surface of one or more of the MWNTs. The selectivefunctionality on the surface of one or more of the MWNTs can include aprotein, a phospholipids, a nucleic acid, an electron mediator, anionophore, or any combination thereof. The protein can include anenzyme, an antibody, or any combination thereof. The nucleic acid caninclude an oligonucleotide, DNA, RNA, or any combination thereof.

The methods may also include at least two of the doped MWNTs comprisedifferent claddings. The methods may include at least a portion of theMWNTs being doped with a functional dopant molecule. The MWNTs maycomprise one or more functional dopant molecules covalently attached tothe graphene surface of the MWNTs. The functional dopant molecules mayinclude an oxide, a hydroxide, a carboxylic acid, an ester, an ether, acarbonyl, an amine, an amide, an epoxide, a halide, or any combinationthereof. At least a portion of the MWNTs may be doped with a covalentbond linkage that is covalently linked to the graphene surface of theMWNT. The covalent bond linkage may include a Schiff base, acarbodi-imide, an amide, or any combination thereof. The functionaldopant molecules may be covalently attached to the graphene surfaceusing a selective functionality. The selective functionality may includea protein, a phospholipids, a nucleic acid, an electron mediator, anionophore, or any combination thereof. The protein may include anenzyme, an antibody, or any combination thereof. The nucleic acid mayinclude an oligonucleotide, DNA, RNA, or any combination thereof.

The methods may include the electrically conductive layer comprises ametal, an electrically conductive polymer, a carbon film, or anycombination thereof. The electrically conductive layer may be capable ofbeing a lead conductor residing between the substrate and a catalystsurmounted to the electrically conductive layer. The electricallyconductive layer may comprise Pt, Au, Ti, W, V, Mo, or any combinationthereof. The metal may comprise a CVD-deposited metal. The CVD-depositedmetal may comprise TiW, Mo, TiN, or any combination thereof. Theelectrically conductive layer can have a layer thickness in the range offrom about 1 nanometer to about 1000 nanometers, in the range of fromabout 10 nanometers to about 100 nanometers, or in the range of fromabout 50 nanometers to about 100 nanometers. The catalyst can compriseFe, Co, Ni, Mo, Ru, Pt, Cr, Pd, Pd, Si, Tb, Se, Cu, Al, Rh, Os, Ir, orany combination or alloy thereof. The catalyst can comprise Pd powder,Ni silicide, Fe—Ni alloy, Fe—Ni—Cr alloy, Mo—Fe alloy film, Fe—Tb alloy,Pd—Se alloy, Cu—Ni alloy, Co—Cu alloy, Al—Fe alloy, Cu—Fe alloy, Fe Nialloy, Alumina-Ni alloy, Alumina-Ni—Cu alloy, or any combinationthereof. The catalyst can comprise an organo-metallic catalyst, aniron-phthalocyanine, a cobalt-phthalocyanine, or any combinationthereof. The catalyst is usually capable of growing MWNTs. The catalystscapable of growing MWNTs includes nickel, cobalt, iron, or anycombination thereof. The catalyst is characterized as having a layerthickness in the range of from about 1 nanometer to about 10,000nanometers, in the range of from about 500 nanometers to about 1000nanometers, or in the range of from about 700 nanometers to about 900nanometers.

The methods may include a doped MWNT assembly comprising a plurality ofdoped MWNTs perpendicularly oriented to the substrate. The doped MWNTscan be oriented parallel to each other. The assembly of doped MWNTs cancomprise a doped MWNT carpet, a doped MWNT array, or any combinationthereof. The electrically conductive layer can comprise a singlecontiguous conductive layer, and the doped MWNT carpet is in electricalcommunication with the single contiguous conductive layer. The dopedMWNT array can comprise an aligned array of nanotubes of a definedgeometry and pitch oriented with respect to the electrically conductivelayer. The assembly of doped MWNTs can comprise an array of doped MWNTs.The catalyst can patterned on the electrically conductive layer, and theassembly of doped MWNTs can be attached to the patterned catalyst. Thecatalyst can be patterned as an array of islands, stripes, circles,squares, rings, triangles, polygons, or any combination thereof.

Antennae assembly field-effect transistors can include a substratecomprising a source and a drain; a gate oxide layer at least partiallysurmounting the substrate, source and drain; an electrically conductivelayer at least partially surmounting the gate oxide layer; and anassembly of doped MWNTs vertically oriented with respect to theelectrically conductive layer.

Sensors can include at least two electrodes situated on a substrate,wherein at least one of the electrodes comprises a doped antennaeassembly electrode, the doped antennae assembly electrode comprising anelectrically conductive layer at least partially surmounting thesubstrate; and an assembly of doped MWNTs vertically oriented withrespect to the electrically conductive layer to provide the dopedantennae assembly electrode. The sensors can include electrodes thatinclude at least one working electrode and at least one referenceelectrode. Sensors can have at least one working electrode comprises adoped antennae assembly electrode. Sensors can have at least onereference electrode comprises a doped antennae assembly electrode. Atleast one working electrode and at least one reference electrode cancomprise a doped antennae assembly electrode. The reference electrodecan be situated on a field-effect transistor. A field-effect transistorcan comprises a source and a drain, the source and drain beingelectrically connected by conductive leads to electrical contactssituated on the substrate. Sensors can include field-effect transistorsthat comprises: a gate oxide layer at least partially surmounting thesubstrate, source and drain; the electrically conductive layer at leastpartially surmounting the gate oxide layer; and having the assembly ofdoped MWNTs vertically oriented with respect to the electricallyconductive layer. Sensors may further comprise a counter electrode.Sensors may further comprise a counter electrode comprises a dopedantennae assembly electrode, a metallic electrode, or any combinationthereof. Sensors may further comprise a metallic electrode that iscomposed of gold, silver, platinum, palladium, copper, iron, titanium,tungsten, or any combination thereof. Sensors may further compriseelectrically conducting leads connecting each of the electrodes to anelectrical contact situated on the substrate.

Patterned Growth of ACNTs by Solid Precursor Assisted CVD

In these examples a fabrication process is provided to grow carbonnanotube selectively in a chemical vapor deposition using anorganic-metallic precursor Iron (II) Phthalocyanine as a catalyst and acarbon source on a given substrate. The process of chemical vapordeposition (CVD) involves the transformation of gaseous molecules intosolid material on the surface of the substrate. Metals, alloys, orpolymeric films can be deposited by the chemical vapor deposition methodand thus ideal for thermal growth of carbon nanotubes. A one step methodis provided to prepare a well aligned carbon nanotube array whichutilizes an organo-metallic precursor which serves as the source ofcarbon as well as the metal catalyst. This example shows that MWNTs donot grow on copper surfaces. This example provides a fabrication methodto pattern copper on a substrate, which method selectively controls thegrowth of the nanotubes. A fabrication method is provided for depositingcopper to prevent growth of carbon nanotubes generated by pyrolysis ofIron (II) Phthalocyanine. A fabrication method is provided forpatterning copper to selectively grow aligned carbon nanotubes generatedby pyrolysis of Iron (II) Phthalocyanine.

In this example, the process starts with a 100 mm p-type silicon waferwith a 1 um thick thermal oxide (FIG. 14A). A 2500 A of polysiliconlayer is deposited at 600 C following by a phosphorus implantation(dose=1E16 J/cm2, energy=100 keV, 7° tilt), and another 2500 A ofpolysilicon layer deposition. The dopant is activated at 1000 C for onehour. The annealed polysilicon should have resistivity of 20-25ohms/square. The polysilicon (FIG. 14B) is patterned using standardlithography technique and etched by reactive ion etching to form thesensing electrode. Next, a 2000 A thick layer of silicon nitride (FIG.14C) is deposited by low pressure chemical vapor deposition acting as aninsulating material. Access holes are patterned and opened by reactiveion etching of silicon nitride (FIG. 14D). A 5000 A thick copper layer(FIG. 14E) is sputtered and is patterned by the reverse mask of theprevious access hole patterns. Copper is then lifted off by soaking intoacetone (FIG. 14F). At this point, the sample surface essentially hastwo types of surface: 1) the conductive polysilicon electrode, and 2)copper masking layer.

ACNTs Growth Procedure:

-   1. The pre-patterned substrate is introduced into the flow reactor    (quartz tube) (refer FIG. 14I).-   2. Iron (II) Phthalocyanine (0.1-0.7 g) is placed in a    quartz/ceramic boat and placed inside the quartz tube.-   3. The system is sealed and flushed with Argon (Ar) (300-500 Sccm)    for 20-30 minutes. This step removes any oxygen present in the    quartz tube and provides an inert reaction atmosphere.-   4. The temperature of the furnace is set at desired growth    temperature which may range from 800-960° C. depending on the size,    density and quality of ACNTs.-   5. As the temperature of the system reaches 800° C. the flow rate of    Ar is reduced to desired flow rate (10-150 Sccm) and H₂ is    introduced in the gas flow at a desired flow rate (10-150 Sccm).    Allow 10 minutes for the gases to mix uniformly inside the reactor.-   6. The gas flow is maintained steady through out the growth process.-   7. Pyrolysis of the Precursor: Once the furnace attains constant set    temperature, the precursor boat is transferred in the temperature    range (450-750° C.) where the pyrolysis of the organo-metallic    precursor is triggered. Iron and carbon source is released into the    gas phase and gets carried into the flow stream by Ar and H₂. (30    sec-2 min)-   8. The carrier gas transports the metal/carbon into the high    temperature zone where the growth of carbon nanotubes on the    substrate takes place. (2-10 min)-   9. After the reaction time, the furnace is shut-off, the H₂ flow is    turned off, and only Ar gas flow is maintained steady at a low flow    rate (300-500 Sccm).-   10. Once the furnace temperature reaches a safe value and all the H₂    is flushed out of the reactor system, the quartz tube is opened and    exposed to air.-   11. The ACNT growth will take place only on chip area which is not    covered with Copper.-   12. The substrate is taken out of the tube and taken for Copper    removal process.

Post-Synthesis Clean Up—Copper Layer Removal Process:

-   1. After the synthesis of ACNTs on the patterned chip (CHEM Chip),    the Cu—sacrificial/growth inhibiting layer has to be removed,    without hindering the alignment and geometry of the carbon    nanotubes.-   2. Cu-removal solution: H₂O:HCl:H₂O₂ in the ratio of 20:0.4:0.2 v/v.    Dip the ACNT coated CHEM Chip in Cu-removal solution with stirring    for 5 min.-   3. Remove the ACNT coated CHEM Chip from the Cu-removal solution and    dip it in DI-H₂O with stirring and allow to clean for 10 min.-   4. After DI-H₂O rinsing, dry the ACNT coated CHEM Chip in air.-   5. The dry ACNT coated CHEM Chip is introduced into the RF Plasma    Asher.-   6. O₂ or H₂O Plasma treatment is carried out to remove residual    organic deposits present on the ACNT coated CHEM Chip. Plasma    Conditions: Power 25-50 W; Pressure 0.9-0.08 mbarr; Time 30 sec-10    min. While this plasma etches away the amorphous carbon, it also    attacks the nanotube to some degree. An alternative fabrication    process could involve depositing an additional silicon dioxide layer    underneath the copper sacrificial layer. The amorphous carbon could    then be lifting off when the sample is soaking in hydrofluoric acid,    while nanotubes remain unattacked.-   7. After the Plasma Clean Up Process, inert SiN layer is exposed and    the ACNT patterned chip is ready for further characterization and    sensor development.

Growth of Aligned/Non-Aligned Carbon Nanotubes by Gas Phase ChemicalVapor Deposition

Carbon nanotubes (CNTs) are synthesized in a thermal CVD system usingArgon (Ar), Ammonia (NH₃)/Hydrogen (H₂) as the carrier gas mixture andAcetylene (C₂H₂) as the carbon source. Gas Phase CVD growth has beensuccessfully established on Nickel metal catalyst and various substrateslike Si, SiO₂, SiN, Poly Si (Phosphorus doped) and P-type Si (BoronDoped). The tubes grown are either aligned or not aligned depending onthe process conditions a substrate preparation. The diameter of thesenanotubes range from 10-40 nm with thick walls and narrow cores. Thegrowth conditions govern the synthesis of predominantly bamboostructured tubes or mixture of bamboo and hollow tubes. This growthprocess is defined by the catalyst and was successfully transferred ontothe patterned chip to yield clean and patterned carbon nanotube growth.Non-aligned CNTs were grown on these substrates at growth temperature of650° C. to 750° C. Aligned CNTs are grown by adding Titanium (Ti) as thebarrier layer in between the substrate (Si) and catalyst (Ni). Titaniumwith thickness of 10-50 nm was deposited on the substrate prior tonickel deposition. The following describes detail experimental processesused to synthesize CNTs in a thermal CVD system.

Substrate Pre-Treatment.

Annealing. Sample annealing at temperature range from 350° C. to 450° C.is used prior to CNTs growth. Sample is introduced inside the furnaceand flushed with Ar gas (100-300 sccm) for 10 minutes. The exhaust ofthe reactor is attached to a vacuum source which creates 10 to 1 Torrpressure inside the reactor. Ar flow is cut-off once vacuum is achievedinside the reactor. The furnace is turned on and temperature is set for350° C. to 450° C. It takes approximately 5 to 7 minutes for the furnaceto reach the set temperature. Heating under vacuum is carried out for 12to 18 hours. At the end of the annealing time the furnace power isturned off and allowed to cool down until it reaches room temperature.The vacuum source is then cut-off and the system is purged with Ar. Thesystem is opened and pre-treated substrate is ready for CNTs growthprocess.

CNTs Growth Processes by Gas Phase CVD.

Annealed substrate is introduced inside the thermal CVD reactor. The CVDreactor is sealed and flushed with Ar gas (100 to 300 Sccm) for 10minutes. After sufficient purging, the furnace power is turned on andthe system is heated under Ar atmosphere until the set temperature (650°C. to 750° C.). Once the growth temperature is reached, Ar gas flow rateis changed to the desired value which can range from 5 to 400 sccmdepending on the substrate combination used and quality of CNTs desired.Etching gas Hydrogen/Ammonia is introduced in the system at a flow rateranging from 10 to 250 sccm. The etching process is carried out for 2 to10 minutes to form nanometer size catalytic particles. After the etchingstep, Acetylene as the carbon source is introduced into the chamber togrow CNTs. The growth time ranges from 5 to 60 minutes. After the growthtime, Acetylene is turned off while Ar and Hydrogen/Ammonia are kept atconstant flow ratio for 1 minute. Then the Hydrogen/Ammonia and furnaceare turned off and the sample is allowed to cool to room temperature inAr (100-300 sccm) atmosphere. After cool down, the system is opened andsample is taken for further examination.

Growth of Aligned Carbon Nanotubes by Solid Precursor Assisted ChemicalVapor Deposition

These examples pertains to a chemical vapor deposition process forgrowing aligned multiwalled carbon nanotube film on a variety ofsubstrates. The chemical vapor deposition recipes adapted for the growthof aligned carbon nanotubes are very specific as they allow for the useof these films as electrodes for sensing applications.

The process of chemical vapor deposition (CVD) involves thetransformation of gaseous molecules into solid material on the surfaceof the substrate. Metals, alloys, or polymeric films can be deposited bythe chemical vapor deposition method and thus ideal for thermal growthof carbon nanotubes. A one step method is developed to prepare a largequantity of well aligned carbon nanotube film without any substratepre-treatment or a preformed template, which utilizes an organo-metallicprecursor as the source of carbon as well as the metal catalyst. Thisone-step production of bundles of aligned carbon nanotube array requiresno prior preparation of the substrate or an external template to directthe alignment. This process allows growth of ACNTs on variety ofconducting as well as insulating substrates like Silicon, Doped Silicon,Poly Silicon, Silicon Nitride, Silicon Oxide etc. Iron (II)Phthalocyanine (FePc) is used as the source which provides metalcatalyst as well as carbon feed for preparing aligned carbon nanotubes.A mixture of Argon (Ar) and Hydrogen (H₂) is used as carrier gas duringthe growth process. The carbon nanotubes grown by this method aremultiwalled carbon nanotubes, with length in the range of 1-50 μm anddiameter in the range of 40-100 nm. The tubes grown are a mixture ofhollow and bamboo structured tubes. The core size of these tubes rangefrom 5-15 nm which is favorable for further doping processes. Traceamount of amorphous carbon have been detected on the side walls of thenanotube, but no apparent interference on the electrode properties hasbeen observed.

ACNT Growth Procedure

-   1. The substrate (quartz slide/silicon chip) is cleaned with    Isopropyl alcohol, dried in air and introduced into the flow reactor    (quartz tube) (refer FIG. 14I).-   2. Iron (II) phthalocyanine (0.1-0.7 g) is placed in a    quartz/ceramic boat and placed inside the quartz tube.-   3. The whole system is sealed and flushed with Argon (Ar) (300-500    Sccm) for 20-30 minutes. This step removes any oxygen present in the    quartz tube and provides an inert reaction atmosphere.-   4. The temperature of the furnace is set at desired growth    temperature which may range from 800-960° C. depending on the size,    density and quality of ACNTs.-   5. As the temperature of the system reaches 800° C. the flow rate of    Ar is reduced to desired flow rate (10-150 Sccm) and H₂ is    introduced in the gas flow at a desired flow rate (10-150 Sccm).    Allow 10 minutes for the gases to mix uniformly inside the reactor.-   6. The gas flow is maintained steady through out the growth process.-   7. Pyrolysis of the Precursor: Once the furnace attains constant set    temperature, the precursor boat is transferred in the temperature    range (450-750° C.) where the pyrolysis of the organo-metallic    precursor is triggered. Iron and carbon source is released into the    gas phase and gets carried into the flow stream by Ar and H₂. (30    sec-2 min)-   8. The carrier gas transports the metal/carbon into the high    temperature zone where the growth of carbon nanotubes on the    substrate takes place. (2-10 min)-   9. After the reaction time, the furnace is shut-off, the H₂ flow is    turned off, and only Ar gas flow is maintained steady at a low flow    rate (300-500 Sccm).-   10. Once the furnace temperature reaches a safe value and all the H₂    is flushed out of the reactor system, the quartz tube is opened and    exposed to air.

The substrate is taken out of the tube and further examination iscarried out (SEM/TEM).

Encapsulation of Catalyst at the Base of the MWNTs

This example provides a fabrication process to insulate mainly thecatalyst at the base of the carbon nanotubes, without insulating the tipor the wall (e.g., mid-section) of the tubes. Such insulation allowselectrochemical response of carbon nanotubes with the sample solutionwhile preventing undesirable electrochemical interaction of the catalystwith the solution. The insulation material also provides additionalmechanical support for carbon nanotubes when the nanotubes are exposedto harsh environment such as high flow.

The MWNTs make an ideal electrode candidate for electrochemicaldetection. Nanotubes can be grown on catalyst such as nickel, iron, andlead. During electrochemical analysis, the catalyst can also be exposedto the solution thus exhibit electrochemical response. In order toprevent such undesirable electrochemical response, the catalyst can beinsulated. This example provides a fabrication method of depositingsilicon nitride as an insulating material for ion sensing application.This example also provides a fabrication method of depositing aninsulating material covering nanotube structures where the insulatingmaterial is patterned by partial exposure of a positive photoresist.Also described is fabrication method for preventing nanotubes fromforming honey-comb structure arising from stiction by supercriticalpoint carbon dioxide drying method.

The processes in this example start with a 100 mm silicon wafer (FIG.17A) with aligned carbon nanotube film. This process can also beapplicable to other substrates such as glass wafers. Next, a 500 A thicksilicon nitride (FIG. 17B) is deposited by plasma-enhanced chemicalvapor deposition at 380 C acting as an insulating material. Otherinsulating material such as silicon oxide can also be used. Depositionmethod is not limited to evaporation, sputtering, thermal, hot wireddeposition. In this application, silicon nitride is used because iteffectively stops ionic molecules in contact with the nanotubes. Afterthat, a positive photoresist (AZ9260) is spin-coated (2K rpm, 20 sec)and soft baked (115 C, 260 sec, hot plated) covering the entirety of thenanotubes (FIG. 17C). The photoresist undergoes partial ultra-violetexposure (300 mW/cm2, 4 sec) (FIG. 17D), such that some photoresist isleft after development (AZ400:DI H20: 1:3, 2.5 min) covering the lowerportion of the nanotubes, while the upper portion of the silicon-nitridecovered nanotubes are exposed. After development of photoresist, thesample might be undergoing supercritical point carbon dioxide drying toprevent nanotubes from sticking to each other forming honey-combstructures due to capillary-induced stiction. Subsequently, the sample(FIG. 17E) is exposed to wet etching such as buffered hydrofluoric acid(2 min) to etch away exposed silicon nitride residing on the sheath ofthe tubes. Finally phororsist (FIG. 17F) is removed by soaking inacetone or other solvents for a short time. The sample might againundergo supercritical point carbon dioxide drying to prevent nanotubesfrom sticking to each other forming honey-corn structures due tocapillary-induced stiction.

Doping of MWNTs by Supercritical Treatment

In these examples, the gas like behavior of supercritical CO₂ is used tospread out along a surface more easily than a true liquid, whilemaintaining the dissolving property of a liquid. The supercritical CO₂transports and encapsulates the molecules/compounds of interest intonanoscopic cavities like that of a hollow nanotube. Successfulencapsulation of interesting molecules/compounds into nanotube cavitieswould give rise to ‘peapod’ like structures. The discussion that followsprovides details of experiments carried out in supercritical medium withACNTs, SWNTs and a target molecule of interest, which has a specificelectrochemical signal. The characterization shows that we were able todope the carbon nanotubes with the target molecule, both inside thehollow core and on the outer walls, while maintaining the electroactivity of the molecule.

A critical point dryer is an instrument for drying materials/samplesusing a supercritical carbon dioxide (CO₂) medium. Carbon dioxide isknown to form a very clean and inert supercritical fluid, which achievessuper criticality at 31° C. and a pressure about 1070 psi.

Procedure—Condition 1:

Substrate/Sample: ACNT film (Solid Precursor CVD), SWNT (commercialsample).

Target molecule:{6}-1-(3-(2-thienylethoxycarbonyl)-propyl)-{5}-1-phenyl-[5,6]-C61.(64BFA)

Solvent: Carbon Disulfide (CS₂)

Temperature: 80° C.

Pressure: 2000 psi

Time: 2 days

Characterization:

The ACNT film and SWNT powder were air oxidized (conditions in lab book)prior to any treatment, in order to create defects (holes) on the wallsof the CNTs. They were characterized with SEM and TEM (FIG. 18A) beforethe supercritical treatment with Condition 1. The electrochemicalbehavior of the ACNT film was also recorder prior to the treatment.

After the supercritical treatment, the samples were thoroughly washedwith CS₂ and MeOH and prepared for further characterization. The treatedACNT film was examined in the SEM and it was evident that there is acoating on the nanotube surface. The TEM evaluation shows that there isa definite coat in/around the carbon nanotubes. To confirm that thetarget molecule is not only present on the surface of the nanotubes, butalso inside the hollow core of the tubes, (energy dispersive X-ray) EDXwas performed. From FIG. 18E, it is evident that there is an increase inthe levels of carbon and sulfur (indicative of the target molecule) inthe centre of the tube.

The SWNT powder sample was characterized with high resolution TEM, wherein the presence of fullerene like molecule structure are visible (FIG.18F).

After the verification that target molecule moieties are present in thecore of the nanotubes, the ACNT sample film was characterizedelectrochemically to check for the specific target molecules. The CVsexhibit specific target molecule signal (FIG. 18G, 18H) providing proofthat the molecule is electrochemically active even after the treatment.

As shown in FIG. 18 (G, H) it is evident from the signature peakobserved at ˜−1.5V that the target molecule 64BFA is present andelectrochemically active on the ACNT film after the supercriticaltreatment.

Condition 2:

Substrate/Sample: ACNT film (Solid Precursor CVD) Target molecule:(6)-1-(3-(2-thienylethoxycarbonyl)-propyl)-{5}-1 phenyl-[5,6]-C61.(64BFA)

Solvent: Carbon Disulfide (CS₂)

Temperature: 40° C.

Pressure: 1200 psi

Time: 5 hrs

ACNT film was treated with Condition 2, in different Critical PointDryer instrument, which had limited temp and press range. The treatmentwas carried out with the same target molecule as in Condition 1. Thefilm was air oxidized (550° C. for 30 sec) prior to any treatment.Supercritical treatment (Condition 2) was carried out in the Bio imagingLab facilities (DBI). The ACNT sample after treatment was thoroughlyrinsed with CS₂ and MeOH solvents, to remove any loosely attachedcompounds. The SEM characterization (FIG. 18I) showed coating on thesurface of the nanotubes (Similar to that observed with Condition 1samples).

The electrochemical response of the film after the treatment was alsorecorded. It was observed that the target molecule specific signals arepresent and that the compound is electro-active. (Ref FIG. 18(G) forsignature electrochemical signal for the target molecule in solution)

Amperometric Reduction of Free Chlorine at Carbon Nanotube Films

When either chlorine gas (Cl₂), hypochlorite solution (NaOCl), or solidCa(OCl)₂ are added to water (for water disinfection), the followingreactions take place

Cl₂+H₂O→HOCl+H⁺+Cl⁻

OCl⁻+H₂O→HOCl+OH⁻

The reduction reaction of the hypochlorite ion at the electrode inaqueous solutions can be described as:

ClO⁻+2e ⁻+H₂O→Cl⁻+2OH⁻

Carbon nanotube electrodes (CNTs) are designed to be electrochemicallyrobust to strong oxidizing agents such as the oxoacids of chlorine. Inthese examples, CNTs were used as working electrodes for the analysis offree chlorine in aqueous solutions using the reduction reaction of freechlorine described above.

The amperometric reduction of ClO− was conducted at 0 V for 5 s. Theresulting charge under the i-t curve was used for quantitation.

A single compartment three electrode glass cell was used. The planar CNTworking electrode was pressed against a viton o-ring and clamped to thebottom of the cell. A graphite rod was used as the counter electrode anda commercial Ag/AgCl (BAS systems) served as a reference electrode (E⁰Ag/AgCl=0.034 V Vs calomel). The geometric area of the working electrodewas ca. 0.2 cm². All measurements were performed at room temperature˜25° C.

Chemicals.

Phosphate buffer was prepared by mixing appropriate volumes of solutionsof 0.05 M sodium phosphate dibasic and 0.05 M sodium phosphate monobasic(Sigma-Aldrich) to yield the desired pH (usually pH 7). Chlorinesolutions were initially prepared from a stock of 5% w/w hypochlorousacid (EMD chemicals Inc.). This “bleach” solution was found to beunstable in spite of being stored at 4° C. and there was ambiguity as toits exact concentration. Henceforth, Free Chlorine Standard (HachVoluette, catalog no. 14268) was used as the stock solution of thehypochlorous acid (initial concentration of HOCl=79.3 ppm or 61.9 ppm).These stock solutions had been commercially prepared by generating anddissolving chlorine gas in slightly alkaline, high purity water of zerochlorine demand. All solutions were prepared in glassware treated tomake them chlorine demand free.

FIG. 19A shows the i-E curves for the electrolysis of 0.1 M ClO⁻ in 0.1M phosphate buffer (pH 6.8) and for the phosphate buffer by itself. Theoxidation peak observed is for the chlorine evolution reaction whichshows an onset potential of about 900 mV at the CNT electrodes.

The cathodic charge observed in the potential range from 0 mV to-500 mVis due to the reduction of the hypochlorite ion/hypochlorous acidspecies according to the listed equations.

FIG. 19B shows typical amperometric reduction curves obtained for thereduction of the free chlorine species in water (solid-phase grown CNT,0.11 cm² inner area of o-ring). These curves are for solutionconcentrations of chlorine ranging from 10 ppb to 10 ppm. Plots of theresulting charge under the curves versus the solution concentration ofchlorine are linear (R²=0.9888 in this case).

The current vs. t^(−1/2) plots also showed a linear relationship,indicating a semi-infinite linear diffusion of the chlorine species toCNT electrodes.

The pH of the solution determines the relative proportions ofhypochlorous acid (HOCl) and hypochlorite ion (OCl⁻). At 0° C. and pH7.9, chlorine is present as half active HOCl and half inactive OCl⁻. Thedissociation reactions of chlorine dissolved in water can be written asfollows:

Cl₂+H₂O→H⁺+Cl⁻+HOCl pK₁=4.6 at 25° C.

HOCl→H⁺+ClO⁻ pK₂=7.5 at 25° C.

FIG. 19C demonstrates the conductivity and pH trends for solutions ofdissolved chlorine.

FIG. 19D demonstrates the effect of electrolyte on the response for thereduction of the hypochlorite ion on CNTs in comparison with acommercial sample of conducting diamond (a model planar electrode).Plots of resultant hypochlorite reduction charge Vs. its solutionconcentration are presented. CNTs are expected to have a minimuminternal iR drop due to their small sizes and good electricalconductivity. Indeed, the ratio of the sensitivities of response with noadded electrolyte was CNT:Diamond 28.5.

Based on these experiments, one can carry out the free chlorinereduction assay on CNT electrodes without addition of electrolyte.

FIG. 19E shows the CNT comparison plot of resultant hypochloritereduction charge Vs. its solution concentration using differentelectrode surfaces such as diamond, glassy carbon (GC) and gold. The R²values were found to be CNT: 0.9997, Au: 0.9996, GC: 0.9853 andconducting diamond: 0.9263. It was found that the sensitivities werehighest for CNTs followed by Au, GC and diamond in that order.

FIG. 19F gives an example of the repeatability of the response of thefree chlorine reduction reaction on CNTs. Here, the plot of trial number(n) versus the resultant charge for the same concentration ofhypochlorite (100 ppb ClO⁻ in 0.05 M phosphate buffer) is shown.

The Coefficient of Variation (%) of a set of values is calculated as:100*(Standard Deviation)/(mean value of set). In this case thecoefficient of variation was found to be 5.25% which is in an acceptablerange.

CNT based sensors for free chlorine have been demonstrated in theseexamples to provide superior sensitivity as compared to conventionallyused electrode materials such as diamond, gold and glassy carbon. Theresponse is precise and the linear dynamic range spans 4-5 orders ofmagnitude. Assays without the addition of supporting electrolyte arealso analytically useful.

Potentiometric Measurement of Calcium Based On a Conducting PolymerCladded MWNT Structure

Ion-selective electrodes are electrochemical sensors that measure a widerange of analytes in aqueous solutions. A solid-contact calciumselective electrode is described that is based on a calcium ionophoredoped conducting polymer CNT cladding. The analytical performance ofthis sensor (potentiometric) was evaluated. When the ionophore doped CNTelectrode was in contact with an aqueous solution containing calcium, anelectrode potential develops across the surface which is dependent onthe level of free calcium ion.

The electrochemical cell consisted of ion selective and referenceelectrodes. The potential difference between the cladded CNT (ionselective) and reference electrode (Silver/Silver chloride) was measuredwith a commercial pH/mV meter. All the measurements were carried out inTris buffer (pH 7.2), and at room temperature (˜25 C). The potentialreadings were taken after stabilization for 1 minute.

Chemicals: 0.05 M Tris Hydroxy methyl amino methane (Fisher, N.J.)buffer (pH 7.2) was used for all the potentiometric measurements.10⁻¹-10⁻⁵M Calcium chloride (Sigma, Mo.) solutions were prepared from0.1 M CaCl₂ stock solution in Tris buffer. Polyaniline (PANI) emeraldinebase powder, Di(2-ethylhexyl)phosphate (H⁺DEHP⁻) and Potassiumtetrakis(4-chlorophenyl)borate KB(ClPh)₄ were purchased from Sigma.Calcium ionophore (ETH 1001) was obtained from EMD Biosciences. All theaqueous solutions were prepared using deionized water.

Referring to FIGS. 20A and 20B, the electrode showed Nernstian responsetoward calcium with a slope of 18.2 mV (ideal theoretical Nernstianslope is 29.5 mV). The undoped PANT film showed a concentrationdependent ionic response. To account for this, the potential differencevalues at each concentration were corrected for the calcium response ofthe doped PANT electrode. Linear response ranges from 10⁻⁴ to 0.1 MCa²⁺. The response is similar to a conventional PVC membrane matrix caston a conducting polymer cladded CNT electrode. Thus, the conductingpolymer by itself can act as a matrix and demonstrate a stable response.Measuring the PANT film with the calcium ionophore, gave rise to theslope of the graph being drastically improved. An overlay of theresponse curve for the doped and undoped PANT electrode is shown in FIG.20B.

Referring to FIG. 20C, the electrode showed Nernstian response towardcalcium with a slope of 26.1 mV. Linear response ranges from 10⁻³ to 0.1M Ca²⁺. There is an order of magnitude difference in the detection limitwith tap water (10 ⁻³ M). The redox and pH sensitivity of the PANTlimits the performance of the sensor. The conductivity of polyaniline isknown to be strongly affected by the oxidation state as well as thedegree of protonation.

Interference Studies.

Selectivity studies of the Calcium selective electrode were carried outwith respect to K⁺, Na⁺ and Mg²⁺ respectively. Mg²⁺ is the major cationthat causes measurement errors in water sensing devices. Both Ca²⁺ andMg²⁺ contribute to the total hardness of water. In regard to measuringwater total hardness, interference from Mg²⁺ apparently does not alterthe sensor performance.

Results.

CNT based sensors provide robust, portable, simple, and relativelyinexpensive methods of analysis. Polymer cladded CNTs can provideminiaturized electrochemical sensors.

1-69. (canceled) 69a. (canceled) 69b. (canceled) 70-77. (canceled)
 78. Amethod of making an antennae assembly electrode, comprising the stepsof: surmounting a substrate with an electrically conductive layer;surmounting an assembly of antennae on the electrically conductive layergiving rise to the antennae being vertically oriented with respect tothe electrically conductive layer, wherein each of the antennaecomprises a MWNT comprising a base end being attached to theelectrically conductive layer; a mid-section comprising an outer surfacesurrounding a lumen, wherein at least a portion of the outer surface ofthe mid-section is capable of being in fluidic contact with anenvironment in contact with the antennae; and a top end being disposedopposite to the base end; and doping at least a portion of the MWNT witha cladding, a covalent bond linkage, a functional dopant molecule, afill material, or any combination thereof.
 79. The method of claim 78,further comprising the step of surmounting the substrate with a thermaloxide layer, wherein the electrically conductive layer surmounts thethermal oxide layer.
 80. The method of claim 79, further comprising thestep of surmounting the thermal oxide layer with an electricallyconductive contact pad.
 81. The method of claim 78, wherein theelectrically conductive layer is surmounted to the substrate using achemical vapor deposition process, a sputtering process, a fluiddeposition process, or any combination thereof.
 82. The method of claim78, wherein a catalyst is surmounted to the electrically conductivelayer using a chemical vapor deposition process, a sputtering process, afluid deposition process, or any combination thereof.
 83. The method ofclaim 82, wherein the chemical vapor deposition process includes a gasphase thermal chemical vapor deposition method, a solid precursorchemical vapor deposition method, a plasma-enhanced chemical vapordeposition method, or any combination thereof.
 84. The method of claim82, wherein the chemical vapor deposition method includes microwavestimulation, radio frequency plasma stimulation, direct current plasmafield enhancement, laser energy enhancement or any combination thereof.85. The method of claim 78, wherein the step of surmounting an assemblyof antennae includes end-linking a plurality of MWNT to the conductivelayer.
 86. The method of claim 85, wherein the plurality of MWNTself-assemble on the conductive layer.
 87. The method of claim 85,wherein the MWNT comprise an end-functionalized MWNT.
 88. The method ofclaim 85, wherein the conductive layer comprises functional groups thatlink to the ends of the MWNT.
 89. The method of claim 88, wherein theMWNT comprise an end-functionalized MWNT.
 90. The method of claim 85,wherein the MWNT are provided as a dispersion of a plurality of MWNT ina fluid.
 91. The method of claim 90, wherein the fluid is an organicliquid, an aqueous liquid, or any combination thereof.
 92. The method ofclaim 78, wherein the step of surmounting an assembly of antennaeincludes growing an assembly of MWNT on the conductive layer.
 93. Themethod of claim 92, wherein the step of growing an assembly of MWNTincludes gas phase thermal vapor deposition, solid precursor chemicalvapor deposition, plasma enhanced chemical vapor deposition, laserenhanced CVD or any combination thereof.
 94. The method of claim 78,wherein the step of surmounting an assembly of antennae includessurmounting the conductive layer with catalyst and contacting a MWNTforming composition and the catalyst at conditions necessary to grow theassembly of MWNT from the catalyst.
 95. The method of claim 94, whereinthe step of growing an assembly of MWNT includes gas phase thermal vapordeposition, solid precursor chemical vapor deposition, plasma enhancedchemical vapor deposition, or any combination thereof.
 96. The method ofclaim 94, wherein the MWNT forming composition comprises, anorganometallic precursor, or any combination thereof.
 97. The method ofclaim 96, wherein the organometallic precursor comprises aphthalocyanine, a porphorin, a carbon bearing ligand, or any combinationthereof.
 98. The method of claim 97, wherein the organometallicprecursor comprises iron(II) phthalocyanine.
 99. The method of claim 97,wherein the carbon bearing ligand comprises a transition metal chelateincluding Fe, Co, Ni, Ru, Os, Eu, or any combination thereof.
 100. Themethod of claim 94, wherein the MWNT forming composition comprises oneor more molecules composed of covalently bonded carbon atoms, hydrogenatoms, oxygen atoms, nitrogen atoms, or any combination thereof. 101.The method of claim 100, wherein the molecules include gases comprisingmethane, ethane, propane, butane, ammonia, acetylene, ethylene,propylene, or any combination thereof.
 102. The method of claim 100,wherein the molecules include liquids comprising aliphatic hydrocarbons,olefins, or any isomer or combination thereof.
 103. The method of claim94, wherein the conditions necessary to form the assembly of MWNTincludes a temperature in the range of from about 300° C. to about 1000°C. and a pressure in the range of from about 10⁻¹ ton to 10⁻⁹ ton. 104.The method of claim 103, wherein the conditions necessary to form theassembly of MWNT includes a temperature in the range of from about 500°C. to about 700° C. and a pressure in the range of from about 10⁻⁶ tonto 10⁻⁹ ton.
 105. The method of claim 103, wherein plasma-enhancedchemical vapor deposition is used to form the MWNT.
 106. The method ofclaim 78, wherein the step of doping includes liquid coating, chemicalvapor deposition, ion beam deposition, electrospray coating,supercritical fluid solute phase transfer, or any combination thereof.107. The method of claim 106, wherein the ion beam deposition includeselectro-spray ionization, electron beam deposition, proton beamdeposition, atomic ion beam deposition, molecular beam deposition, orany combination thereof.
 108. The method of claim 78, further comprisingthe step of depositing a metal on the electrically conductive layer toprovide an electrode contact pad.
 109. The method of claim 108, whereinthe electrode contact pad is distally located from the assembly of MWNT.110. The method of claim 78, further comprising the step of patterningthe assembly of MWNT.
 111. The method of claim 110, wherein the step ofpatterning gives rise to an array of MWNT.
 112. The method of claim 110,wherein the step of patterning includes photolithography, UVlithography, e-beam lithography, reactive ion etching, chemical etching,nano-imprinting, electro-forming, or any combination thereof.
 113. Themethod of claim 78, further comprising the step of patterning theelectrically conductive layer.
 114. The method of claim 113, wherein thestep of patterning gives rise to an array of MWNT.
 115. The method ofclaim 113, wherein the step of patterning includes photolithography, UVlithography, e-beam lithography, reactive ion etching, chemical etching,nano-imprinting, electro-forming, electrochemical polymerization, or anycombination thereof.
 116. The method of claim 78, wherein the step ofsurmounting the substrate with an electrically conductive layer includeselectroforming, electro-less deposition, electrochemical deposition,vapor deposition, sputtering, or any combination thereof.
 117. Themethod of claim 78, wherein the assembly of doped MWNT comprise aplurality of MWNT having a fill material.
 118. The method of claim 117,wherein the fill material includes molecules, molecular ions, atoms,atomic ions, or any combination thereof.
 119. The method of claim 117,wherein the fill material includes one or more fullerenes, dopedfullerenes, ionophores, ion exchangers, redox molecules, conductivepolymers, or any combination thereof.
 120. The method of claim 119,wherein the ionophores include cyclic polyethers, antibiotics, linearchain ligands or any combination thereof.
 121. The method of claim 120,wherein the cyclic polyethers comprise 12-crown-4 to 24-crown-8polyethers, or any combination thereof.
 122. The method of claim 120,wherein the ionophores includes one or more cryptands, calixarenes,rotaxanes, or any combination thereof.
 123. The method of claim 119,wherein the fullerenes include one or more of C₆₀, C₇₀, C₈₀, C₉₀, or anycombination thereof.
 124. The method of claim 119, wherein thefullerenes are doped fullerenes.
 125. The method of claim 124, whereinthe doped fullerenes are filled, coated, chemically functionalized, orany combination thereof.
 126. The method of claim 119, wherein the ionexchangers include quaternized PVC, sulfonated TPFE, or any combinationthereof.
 127. The method of claim 120, wherein the antibiotics includevalinomycin, nonactin, monensin, iosin, or any combination thereof. 128.The method of claim 120, wherein the linear chain ligands includepoly-oxyethylene, tri-n-alkylammonium halide,N,N,N′,N′-Tetrabutyl-3,6-dioxaoctanedi(thioamide),N,N,N′,N′-tetracyclohexyl-3-oxapentadienediamide,alkyl-4-trifluoroacetylbenzoate, tridodecylamine, or any combinationthereof.
 129. The method of claim 117, wherein the fill materialincludes semiconductor polymers comprising donor-acceptor pairs. 130.The method of claim 129, wherein the semiconductor polymers comprisedonor-acceptor pairs include semicarbazole/TCNQ, ionene/iodine, or anycombination thereof.
 131. The method of claim 117, wherein the fillmaterial includes conductive polymers.
 132. The method of claim 131,wherein the conductive polymers comprise a polypyrrole, a polyaniline, apoly-p-phenylene, a polyacetylene, a polythiophene, or any combinationthereof.
 133. The method of claim 117, wherein at least two of the dopedMWNT comprise different fill molecules.
 134. The method of claim 117,wherein the fill material includes a chemical agent capable ofresponding to a chemical or an electrical signal.
 135. The method ofclaim 78, wherein at least a portion of the MWNT are doped with acladding.
 136. The method of claim 135, wherein the cladding includes adielectric, an ion conducting polymer, an electron conducting polymer,an ionophore polymer dopant, a redox-mediator dopant, or any combinationthereof.
 137. The method of claim 136, wherein the dielectric includes apolyolefin polymer, a polyaliphatic polymer, a polysiloxane polymer, apolyurethane polymer, a polyvinylchloride polymer, alumina, or anycombination thereof.
 138. The method of claim 136, wherein the ionconducting polymer includes nafion, polystyrene sulfonate,polyvinylpridinium, or any combination thereof.
 139. The method of claim136, wherein the electron conducting polymer includes a doped polymer,an electrochemically doped polymer, a redox electroactive polymer, orany combination thereof.
 140. The method of claim 139, wherein the dopedpolymer includes a polyionine, a polysilicon, a polysemicarbazole, apolyphenylene, a polyacetylene, a polyphenylene sulfide, or anycombination thereof.
 141. The method of claim 140, wherein the dopedpolymer includes a dopant, the dopant comprising AsF₅, I₂, Li, K, BF₆₋,PF₆₋, or any combination thereof.
 142. The method of claim 139, whereinthe electrochemically doped polymer includes a polypyrrole, apolythiophene, a polyphenylquinone, a polyaniline, or any combinationthereof.
 143. The method of claim 139, wherein the redox electroactivepolymers include polyviologen, polyvinylferrocene, poly-Ru(vbpy)3++, orany combination thereof.
 144. The method of claim 136, wherein theionophore polymer dopant includes a crown ether, a cryptand, asphereand, a rotaxane, an antibiotic, a non-cyclic ligand, or anycombination thereof.
 145. The method of claim 136, wherein theredox-mediator dopant includes Ru(bpy)3++, Br2/Br−, Fe(phen)3+++,Co(terpy)2+++, Fe(CN)6(3−), Ru(NH3)6+++, quinone, hydroquinone,methylviologen, tetracyanoquinodimethane, benzophenone, ferrocene,tetramethyl-p-phenylenediamine, tetrathiafulvalene, tri-N-p-tolylamine,or any combination thereof.
 146. The method of claim 135, wherein thecladding comprises one or more functional reactive groups residing upona surface of the cladding.
 147. The method of claim 146, wherein thefunctional reactive groups include an oxide, a hydroxide, a carboxylicacid, an ester, an ether, a carbonyl, an amine, an amide, an epoxide, ahalide, or any combination thereof.
 148. The method of claim 135,wherein the cladding includes a covalent bond linkage attaching thecladding to the doped MWNT.
 149. The method of claim 148, wherein thecovalent bond linkage includes a Schiff base, a carbodi-imide, an amide,or any combination thereof.
 150. The method of claim 135, wherein thecladding is linked to a selective functionality on the surface of one ormore of the MWNT.
 151. The method of claim 150, wherein the selectivefunctionality on the surface of one or more of the MWNT includes aprotein, a phospholipids, a nucleic acid, an electron mediator, anionophore, or any combination thereof.
 152. The method of claim 151,wherein the protein includes an enzyme, an antibody, an antigen or anycombination thereof.
 153. The method of claim 151, wherein the nucleicacid includes an oligonucleotide, DNA, RNA, or any combination thereof.154. The method of claim 135, wherein at least two of the doped MWNTcomprise different claddings.
 155. (canceled)
 156. The method of claim78, wherein at least a portion of the MWNT are doped with a functionaldopant molecule.
 157. The method of claim 156, wherein the MWNT compriseone or more functional dopant molecules covalently attached to thegraphene surface of the MWNT.
 158. The method of claim 157, wherein thefunctional dopant molecules include an oxide, a hydroxide, a carboxylicacid, an ester, an ether, a carbonyl, an amine, an amide, an epoxide, ahalide, or any combination thereof.
 159. The method of claim 78, whereinat least a portion of the MWNT are doped with a covalent bond linkagethat is covalently linked to the graphene surface of the MWNT.
 160. Themethod of claim 159, wherein the covalent bond linkage includes a Schiffbase, a carbodi-imide, an amide, or any combination thereof.
 161. Themethod of claim 156, wherein the functional dopant molecules covalentlyattached to the graphene surface using a selective functionality. 162.The method of claim 161, wherein the selective functionality includes aprotein, a phospholipids, a nucleic acid, an electron mediator, anionophore, or any combination thereof.
 163. The method of claim 162,wherein the protein includes an enzyme, an antibody, or any combinationthereof.
 164. The method of claim 162, wherein the nucleic acid includesan oligonucleotide, DNA, RNA, or any combination thereof.
 165. Themethod of claim 78, wherein the electrically conductive layer comprisesa metal, an electrically conductive polymer, a carbon film, or anycombination thereof.
 166. The method of claim 165, wherein theelectrically conductive layer is capable of being a lead conductorresiding between the substrate and a catalyst surmounted to theelectrically conductive layer.
 167. The method of claim 78, wherein theelectrically conductive layer comprises Pt, Au, Ti, W, V, Mo, or anycombination thereof.
 168. The method of claim 167, wherein the metalcomprises a CVD-deposited metal.
 169. The method of claim 167, whereinthe CVD-deposited metal comprises TiW, Mo, TiN, or any combinationthereof.
 170. The method of claim 78, wherein the electricallyconductive layer is characterized as having a layer thickness in therange of from about 1 nanometer to about 1000 nanometers.
 171. Themethod of claim 78, wherein the electrically conductive layer ischaracterized as having a layer thickness in the range of from about 10nanometers to about 100 nanometers.
 172. The method of claim 78, whereinthe electrically conductive layer is characterized as having a layerthickness in the range of from about 50 nanometers to about 100nanometers.
 173. The method of claim 78, wherein the catalyst comprisesFe, Co, Ni, Mo, Ru, Pt, Cr, Pd, Si, Tb, Se, Cu, Al, Rh, Os, Ir, or anycombination or alloy thereof.
 174. The method of claim 173, wherein thecatalyst comprises Pd powder, Ni silicide, Fe—Ni alloy, Fe—Ni—Cr alloy,Mo—Fe alloy film, Fe—Tb alloy, Pd—Se alloy, Cu—Ni alloy, Co—Cu alloy,Al—Fe alloy, Cu—Fe alloy, Fe—Ni alloy, Alumina-Ni alloy, Alumina-Ni—Cualloy, or any combination thereof.
 175. The method of claim 173, whereinthe catalyst comprises an organo-metallic catalyst, aniron-phthalocyanine, a cobalt-phthalocyanine, or any combinationthereof.
 176. The method of claim 173, wherein the catalyst comprises acatalysts capable of growing MWNT.
 177. The method of claim 176, whereinthe catalysts capable of growing MWNT includes nickel, cobalt, iron, orany combination thereof.
 178. The method of claim 82, wherein thecatalyst is characterized as having a layer thickness in the range offrom about 1 nanometer to about 10,000 nanometers.
 179. The method ofclaim 178, wherein the catalyst is characterized as having a layerthickness in the range of from about 500 nanometers to about 1000nanometers.
 180. The method of claim 179, wherein the catalyst ischaracterized as having a layer thickness in the range of from about 700nanometers to about 900 nanometers.
 181. The method of claim 78, whereinthe doped antennae assembly comprises a plurality of doped MWNTperpendicularly oriented to the substrate.
 182. The method of claim 181,wherein the doped MWNT are oriented parallel to each other.
 183. Themethod of claim 78, wherein the assembly of doped MWNT comprises a dopedMWNT carpet, a doped MWNT array, or any combination thereof.
 184. Themethod of claim 183, wherein the electrically conductive layer comprisesa single contiguous conductive layer, and the doped MWNT carpet is inelectrical communication with the single contiguous conductive layer.185. The method of claim 183, wherein the doped MWNT array comprises analigned array of nanotubes of a defined geometry and pitch oriented withrespect to the electrically conductive layer.
 186. The method of claim78, wherein the assembly of doped MWNT comprises an array of doped MWNT.187. The method of claim 82, wherein the catalyst is patterned on theelectrically conductive layer, and the assembly of doped MWNT isattached to the patterned catalyst.
 188. The method of claim 82, whereinthe catalyst is patterned as an array of islands, stripes, circles,squares, rings, triangles, polygons, or any combination thereof.
 189. Anantennae assembly electrode made according to the method of claim 78.190. (canceled)
 191. (canceled)
 192. An antennae assembly field-effecttransistor, comprising: a substrate comprising a source and a drain; agate oxide layer at least partially surmounting the substrate, sourceand drain; an electrically conductive layer at least partiallysurmounting the gate oxide layer; and an assembly of doped MWNT antennaevertically oriented with respect to the electrically conductive layer.193. A sensor, comprising: at least two electrodes situated on asubstrate, wherein at least one of the electrodes comprises an antennaeassembly electrode, wherein the antennae assembly electrode comprises anelectrically conductive layer at least partially surmounting asubstrate; and an assembly of doped antennae vertically oriented withrespect to the electrically conductive layer, wherein each of the dopedantennae comprises a doped MWNT comprising: a base end attached to theelectrically conductive layer, a mid-section comprising an outer surfacesurrounding a lumen, wherein at least a portion of the outer surface ofthe mid-section is capable of being in fluidic contact with anenvironment in contact with the antennae; a top end disposed opposite tothe base end, and a dopant attached to or contained within the lumen, adopant attached to or contained within the outer surface, a dopantattached to or contained with the top end, or any combination thereof.194. The sensor of claim 193, wherein the electrodes include at leastone working electrode, at least one reference electrode, or both. 195.The sensor of claim 194, wherein at least one working electrodecomprises a antennae assembly electrode.
 196. The sensor of claim 194,wherein at least one reference electrode comprises a antennae assemblyelectrode.
 197. The sensor of claim 194, wherein at least one workingelectrode and at least one reference electrode comprises a antennaeassembly electrode.
 198. The sensor of claim 194, wherein the referenceelectrode is situated on a field-effect transistor.
 199. The sensor ofclaim 198, wherein the field-effect transistor comprises a source and adrain, the source and drain being electrically connected by conductiveleads to electrical contacts situated on the substrate.
 200. The sensorof claim 199, wherein the filed-effect transistor comprises: a gateoxide layer at least partially surmounting the substrate, source anddrain; the electrically conductive layer at least partially surmountingthe gate oxide layer; and the assembly of doped MWNT vertically orientedwith respect to the electrically conductive layer.
 201. The sensor ofclaim 193, further comprising a counter electrode.
 202. The sensor ofclaim 201, wherein the counter electrode comprises a antennae assemblyelectrode, a metallic electrode, or any combination thereof.
 203. Thesensor of claim 202, wherein the metallic electrode is composed of gold,silver, platinum, palladium, copper, iron, titanium, tungsten, or anycombination thereof.
 204. The sensor of claim 201, further comprisingelectrically conducting leads connecting each of the electrodes to anelectrical contact situated on the substrate. 205-207. (canceled) 208.The antennae assembly electrode of claim 3, wherein the metals comprisea metal atom, a metal oxide, a metal halide, a metal alloy, or anycombination thereof.
 209. The antennae assembly electrode of claim 3,wherein the metal comprises Ag, Au, Zn, Cu, or any combination thereof.210-211. (canceled)
 212. A method of making an antennae assemblyelectrode, comprising the steps of: surmounting a substrate with anelectrically conductive layer; and surmounting an assembly of antennaeon the electrically conductive layer giving rise to the antennae beingvertically oriented with respect to the electrically conductive layer,wherein each of the antennae comprises a MWNT comprising a base endbeing attached to the electrically conductive layer; a mid-sectioncomprising an outer surface surrounding a lumen; and a top end beingdisposed opposite to the base end.
 213. The method according to claim212, further comprising doping at least a portion of the MWNT with acladding, a covalent bond linkage, a functional dopant molecule, a fillmaterial, or any combination thereof.
 214. The method according to claim212, further comprising: conformally depositing an insulating materialon each of the antennae and the electrically conductive layer;depositing a photoresist layer on the insulating material; imaging atleast a portion of the photoresist to give rise to an imaged photoresistportion and an unimaged photoresist portion; removing a portion of theimaged photoresist portion or the unimaged photoresist portion to exposethe insulating material conformally deposited on the top end of the MWNTand a portion of the mid-section of the MWNT; and removing theinsulating material conformally deposited on the top end of the MWNT anda portion of the mid-section of the MWNT to give rise to an exposed topportion of the MWNT.
 215. The method of claim 212, further comprisingcontacting the exposed top portion of the MWNT with a super criticalsolution comprising a super critical solvent and a dopant.
 216. A methodof growing non-aligned MWNTs on a substrate, comprising: depositing anickel metal catalyst on a substrate; and contacting the nickel metalcatalyst with a gas mixture comprising a carrier gas and a carbon sourcegas at a temperature in the range of from about 650° C. to about 750°C., the carbon source gas comprising acetylene, wherein the substratecomprises silicon, silicon dioxide, silicon nitride, phosphorus dopedpoly silicon, or boron doped P-type silicon, to give rise to non-alignedMWNTs attached to the nickel metal catalyst.
 217. A method of growingaligned MWNTs on a substrate, comprising: contacting a substrate with agas comprising a carrier gas and a carbon source gas at a temperature inthe range of from about 800° C. to about 960° C., the carbon source gascomprising iron (II) phthalocyanine, wherein the substrate comprisessilicon, silicon dioxide, silicon nitride, phosphorus doped polysilicon, or boron doped P-type silicon, to give rise to aligned MWNTsattached to the substrate.
 218. The method of claim 217, wherein atleast a portion of the substrate comprises a copper pattern, wherebyessentially no MWNTs grow on the copper pattern.
 219. A method ofgrowing aligned MWNTs on a substrate, comprising: depositing a nickelmetal catalyst on the titanium barrier layer; and contacting the nickelmetal catalyst with a gas mixture comprising a carrier gas and a carbonsource gas at a temperature in the range of from about 650° C. to about750° C., the carrier gas comprising argon, ammonia and hydrogen, thecarbon source gas comprising acetylene, wherein the substrate comprisessilicon, silicon dioxide, silicon nitride, phosphorus doped polysilicon, or boron doped P-type silicon, to give rise to aligned MWNTsattached to the nickel metal catalyst. 220-224. (canceled)
 225. Theantennae assembly electrode of claim 69, wherein the pitch is defined asthe ratio of the center to center distance of the MWNTs to the diameterof a MWNT, the pitch being in the range of from about 1:1 to about100:1.
 226. The antennae assembly electrode of claim 69, wherein thelength to diameter aspect ratio of the MWNTs is in the range of fromabout 1:1 to about 10,000:1